





Internet Engineering Task Force (IETF)                        T. Clausen
Request for Comments: 6130                      LIX, Ecole Polytechnique
Category: Standards Track                                    C. Dearlove
ISSN: 2070-1721                                          BAE Systems ATC
                                                                 J. Dean
                                               Naval Research Laboratory
                                                              April 2011


  Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)

Abstract

   This document describes a 1-hop and symmetric 2-hop neighborhood
   discovery protocol (NHDP) for mobile ad hoc networks (MANETs).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6130.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this



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   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

  1. Introduction .....................................................4
      1.1. Motivation .................................................5
   2. Terminology .....................................................6
   3. Applicability Statement .........................................9
   4. Protocol Overview and Functioning ..............................10
      4.1. Routers and Interfaces ....................................11
      4.2. Information Base Overview .................................12
           4.2.1. Local Information Base .............................13
           4.2.2. Interface Information Bases ........................13
           4.2.3. Neighbor Information Base ..........................14
      4.3. Signaling Overview ........................................14
           4.3.1. HELLO Message Generation ...........................15
           4.3.2. HELLO Message Content ..............................16
           4.3.3. HELLO Message Processing ...........................17
      4.4. Link Quality ..............................................17
   5. Protocol Parameters and Constants ..............................18
      5.1. Protocol and Port Numbers .................................18
      5.2. Multicast Address .........................................18
      5.3. Interface Parameters ......................................18
           5.3.1. Message Intervals ..................................19
           5.3.2. Information Validity Times .........................21
           5.3.3. Link Quality .......................................22
           5.3.4. Jitter .............................................22
      5.4. Router Parameters .........................................23
           5.4.1. Information Validity Time ..........................23
      5.5. Parameter Change Constraints ..............................23
      5.6. Constants .................................................24
   6. Local Information Base .........................................24
      6.1. Local Interface Set .......................................25
      6.2. Removed Interface Address Set .............................26
   7. Interface Information Bases ....................................26
      7.1. Link Set ..................................................27
      7.2. 2-Hop Set .................................................28
   8. Neighbor Information Base ......................................28
      8.1. Neighbor Set ..............................................28
      8.2. Lost Neighbor Set .........................................29
   9. Local Information Base Changes .................................29



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      9.1. Adding an Interface .......................................29
      9.2. Removing an Interface .....................................30
      9.3. Adding a Network Address to an Interface ..................30
      9.4. Removing a Network Address from an Interface ..............31
   10. Packets and Messages ..........................................32
      10.1. HELLO Messages ...........................................32
           10.1.1. Address Blocks ....................................33
   11. HELLO Message Generation ......................................34
      11.1. HELLO Message Specification ..............................35
      11.2. HELLO Message Transmission ...............................37
           11.2.1. HELLO Message Jitter ..............................37
   12. HELLO Message Processing ......................................38
      12.1. Invalid Message ..........................................38
      12.2. Definitions ..............................................40
      12.3. Updating the Neighbor Set ................................41
      12.4. Updating the Lost Neighbor Set ...........................42
      12.5. Updating the Link Sets ...................................42
      12.6. Updating the 2-Hop Set ...................................44
   13. Other Information Base Changes ................................45
      13.1. Link Tuple Symmetric .....................................46
      13.2. Link Tuple Not Symmetric .................................47
      13.3. Link Tuple Heard Timeout .................................48
   14. Link Quality ..................................................48
      14.1. Deployment without Link Quality ..........................49
      14.2. Basic Principles of Link Quality .........................49
      14.3. When Link Quality Changes ................................50
      14.4. Updating Link Quality ....................................51
   15. Proposed Values for Parameters and Constants ..................51
      15.1. Message Interval Interface Parameters ....................51
      15.2. Information Validity Time Interface Parameters ...........51
      15.3. Information Validity Time Router Parameters ..............52
      15.4. Link Quality Interface Parameters ........................52
      15.5. Jitter Interface Parameters ..............................52
      15.6. Constants ................................................52
   16. Usage with Other Protocols ....................................52
   17. Security Considerations .......................................54
      17.1. Invalid HELLO Messages ...................................56
      17.2. Authentication, Integrity, and Confidentiality
            Suggestions ..............................................57
   18. IANA Considerations ...........................................57
      18.1. Expert Review: Evaluation Guidelines .....................58
      18.2. Message Types ............................................58
      18.3. Message-Type-Specific TLV Type Registries ................58
      18.4. Address Block TLV Types ..................................59
      18.5. LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB Values ...........60
   19. Contributors ..................................................61
   20. Acknowledgments ...............................................61
   21. References ....................................................62



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      21.1. Normative References .....................................62
      21.2. Informative References ...................................62
   Appendix A. Address Block TLV Combinations ........................63
   Appendix B. Constraints ...........................................64
   Appendix C. HELLO Message Example .................................66
   Appendix D. Flow and Congestion Control ...........................69
   Appendix E. Interval and Timer Illustrations ......................70
      E.1.  HELLO Message Generation Timing ..........................70
      E.2.  HELLO Message Processing Timing ..........................76
      E.3.  Other HELLO Message Timing ...............................77
   Appendix F.  Topology Pictures ....................................79
      F.1.  Example 1: Standard Single Interface Topology ............79
      F.2.  Example 2: Dual Addressed Interface on 1-Hop Neighbor ....80
      F.3.  Example 3: Dual Addressed Interface on 2-Hop Neighbor ....81
      F.4.  Example 4: Dual Addressed Interfaces .....................81
      F.5.  Example 5: Dual Interface on 2-Hop Neighbor ..............82
      F.6.  Example 6: Dual interface on 1-Hop Neighbor ..............82
      F.7.  Example 7: Dual Interface on 1-Hop and 2-Hop Neighbors ...83
      F.8.  Example 8: Dual Interface Locally and on 1-Hop Neighbor ..84
      F.9.  Example 9: Dual Interface on All Routers .................85
      F.10. Example 10: Dual Addressed Dual Interfaces on All
                        Routers ......................................86
      F.11. Example 11: Single Addressed Dual Interface Locally ......87

1.  Introduction

   This document describes a neighborhood discovery protocol (NHDP) for
   a mobile ad hoc network (MANET) [RFC2501].  This protocol uses a
   local exchange of HELLO messages so that each router can determine
   the presence of, and connectivity to, its 1-hop and symmetric 2-hop
   neighbors.  Messages are defined and sent in packets according to the
   specification [RFC5444].

   1-hop neighborhood information is recorded for use by MANET routing
   protocols to determine direct (1-hop) connectivity to neighboring
   routers. 2-hop symmetric neighborhood information is recorded so as
   to enable MANET routing protocols to employ flooding reduction
   techniques, e.g., to select reduced relay sets for efficient network-
   wide traffic dissemination.

   1-hop and symmetric 2-hop neighborhood information is recorded in the
   form of Information Bases.  These are available for use by other
   protocols, such as MANET routing protocols, that require information
   regarding the local network connectivity.  This protocol is designed
   to maintain the information in these Information Bases even in the
   presence of a dynamic network topology and wireless communication
   channel characteristics.




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   This protocol makes no assumptions about the underlying link layer,
   other than support of local broadcast or multicast for communication
   to 1-hop neighbor routers.  Link-layer information may be used if
   available and applicable.

   This protocol is based on the neighborhood discovery process
   contained in the Optimized Link State Routing (OLSR) Protocol
   [RFC3626].

1.1.  Motivation

   MANETs differ from more traditional wired and infrastructure-based
   wireless networks due to their envisioned applicability over more
   challenging communication channels (e.g., wireless, lossy, broadcast
   channels with moderate and shared bandwidth, hidden and exposed
   terminals, and interference from other network devices and the
   environment) and in more challenging topological conditions (e.g.,
   rapid and unpredictable mobility, dynamic and non-predetermined
   network membership).

   Due to the properties of wireless transmissions, communication
   between two neighboring routers may not be bi-directional; even if
   router A is able to receive packets from router B, the converse is
   not guaranteed to be true.  Furthermore, because of the localized
   nature of wireless broadcast communication, neighboring routers
   within the same communications channel may have different sets of
   neighbors.  That is, when using the same communication channel, even
   if router A is able to exchange packets with router B, and router B
   is able to exchange packets with router C, this does not guarantee
   that router A and router C can exchange packets directly.

   Each router in a MANET may use more than one communication channel.
   In particular, between the same pair of routers, more than one
   distinct communication channel may exist, each with different
   properties.  This may, for example, be the case where MANET routers
   are equipped with multiple distinct wireless interfaces, operating at
   different frequencies.

   For use by MANET routing protocols, as well as for establishing a
   router's neighbors, a router may also need to determine whether each
   communication channel with that neighbor is bi-directional.

   The set of neighbor routers of a given MANET router may be
   continuously changing, often due to router mobility or a changing
   physical environment in which the MANET is located.  There is
   typically no information from lower layers that would enable an IP
   routing protocol to detect and, as appropriate, react to such
   changes.  Such changes can often take place on a short timescale,



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   such as of the order of seconds, requiring MANET routing protocols to
   act rapidly to ensure suitable convergence properties.

   MANET routing protocols, for example [RFC3626] and [RFC5449], often
   employ relay set reductions in order to conserve network capacity
   when maintaining network-wide topological information, with
   calculation of these reduced relay sets employing up to two hop
   information.

   The neighborhood discovery protocol specified in this document
   provides continued tracking of neighborhood changes, link bi-
   directionality, and local topological information up to two hops.
   Combined, this allows a MANET routing protocol access to information
   describing link establishment/disappearance and provides the
   necessary topological information for reduced relay set selection and
   other purposes.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   All terms introduced in [RFC5444], including "packet", "message",
   "Address Block", "TLV Block", "TLV", "address", "address prefix", and
   "address object" are to be interpreted as described therein.

   Additionally, this document uses the following terminology:

   Network Address:
      An address plus an associated prefix length.  This may be an
      address with an associated maximum prefix length or an address
      prefix including a prefix length.  A network address thus
      represents a range of addresses.

   Router:
      A MANET router that implements this neighborhood discovery
      protocol.

   Interface:
      A router's attachment to a communications medium.  An interface is
      assigned one or more addresses.

   MANET interface:
      An interface participating in a MANET and using this neighborhood
      discovery protocol.  A router may have several MANET interfaces.




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   Heard:
      A MANET interface of router X is considered heard on a MANET
      interface of a router Y if the latter can receive control
      messages, according to this specification, from the former.

   Link:
      A link between two MANET interfaces exists if either can be heard
      by the other.

   Symmetric link:
      A symmetric link between two MANET interfaces exists if both can
      be heard by the other.

   1-hop neighbor:
      A router X is a 1-hop neighbor of a router Y if a MANET interface
      of router X is heard by a MANET interface of router Y.

   Symmetric 1-hop neighbor:
      A router X is a symmetric 1-hop neighbor of a router Y if a
      symmetric link exists between a MANET interface on router X and a
      MANET interface on router Y.

   2-hop neighbor:
      A router X is a 2-hop neighbor of a router Y if router X is a
      1-hop neighbor of a 1-hop neighbor of router Y, but is not router
      Y itself.

   Symmetric 2-hop neighbor:
      A router X is a symmetric 2-hop neighbor of a router Y if router X
      is a symmetric 1-hop neighbor of a symmetric 1-hop neighbor of
      router Y, but is not router Y itself.

   1-hop neighborhood:
      The 1-hop neighborhood of a router X is the set of the 1-hop
      neighbors of router X.

   Symmetric 1-hop neighborhood:
      The symmetric 1-hop neighborhood of a router X is the set of the
      symmetric 1-hop neighbors of router X.

   2-hop neighborhood:
      The 2-hop neighborhood of a router X is the set of the 2-hop
      neighbors of router X. (This may include routers in the 1-hop
      neighborhood of router X.)







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   Symmetric 2-hop neighborhood:
      The symmetric 2-hop neighborhood of a router X is the set of the
      symmetric 2-hop neighbors of router X. (This may include routers
      in the 1-hop neighborhood, or even in the symmetric 1-hop
      neighborhood, of router X.)

   Constant:
      A numerical value that MUST be the same for all MANET interfaces
      of all routers in the MANET, at all times.

   Interface parameter:
      A boolean or numerical value, specified separately for each MANET
      interface of each router.  A router MAY change interface parameter
      values at any time, subject to some constraints.

   Router parameter:
      A boolean or numerical value, specified for each router, and not
      specific to an interface.  A router MAY change router parameter
      values at any time, subject to some constraints.

   Information Base:
      A collection of information maintained by this protocol and which
      is to be made available to MANET routing protocols.  An
      Information Base may be associated with a MANET interface or with
      a router.

   Furthermore, this document uses the following notational conventions:

   X contains y, or y is contained in X
      An unordered list membership operator.  X is an unordered list and
      y is an element.  "X contains y" or "y is contained in X" returns
      true if the unordered list X includes the element y, and returns
      false otherwise.

   X contains Y, or Y is contained in X
      An unordered list inclusion operator.  X and Y are both unordered
      lists.  "X contains Y" or "Y is contained in X" returns true if
      the unordered list X contains all elements y which are contained
      in Y, and returns false otherwise.

   A overlaps B
      If A and B are network addresses, and the range of addresses
      represented by A and the range of addresses represented by B both
      contain at least one common address.  (This is only possible if
      one range is a sub-range of the other.)






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   a := b
      An assignment operator, whereby the left side (a) is assigned the
      value of the right side (b). a and b may be values, network
      addresses, or unordered lists (they must be of the same type).

   c = d
      A comparison operator, returning true if the value of the left
      side (c) is equal to the value of the right side (d). c and d may
      be values, network addresses, or unordered lists (they must be of
      the same type).  If c and d are unordered lists, then they are
      considered to be equal if c contains d and d contains c (i.e.,
      they contain the same set of elements, regardless of the order in
      which they are recorded in the lists).  If c and d are network
      addresses, they are considered equal only if both addresses and
      prefix lengths are equal (i.e., they represent the same).

   e != f
      A comparison operator, returning not (e = f), i.e., returning true
      where (e = f) would have returned false, and returning false where
      (e = f) would have returned true.

3.  Applicability Statement

   This protocol:

   o  Is applicable to networks, especially wireless networks, in which
      unknown neighbors can be reached by local broadcast or multicast
      packets.

   o  Is designed to work in networks with a dynamic topology, and in
      which messages may be lost, such as due to collisions in wireless
      networks.

   o  Supports routers that each have one or more participating MANET
      interfaces.  The set of a router's interfaces may change over
      time.  Each interface may have one or more associated network
      addresses, and these may also be dynamically changing.

   o  Provides each router with current local topology information up to
      two hops away, and makes this local topology information available
      to MANET routing protocols in Information Bases.

   o  Uses the packet and message formats specified in [RFC5444].  This
      includes the definition of a HELLO Message Type, used for
      signaling local topology information.

   o  Allows "external" and "internal" extensibility as enabled by
      [RFC5444].



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   o  May interact with, and be extended by, other protocols, such as
      MANET routing protocols, see Section 16.

   o  Can use relevant link-layer information if it is available.

   o  Is designed to work in a completely distributed manner, and does
      not depend on any central entity.

4.  Protocol Overview and Functioning

   The objective of this protocol is, for each router:

   o  To identify 1-hop neighbors and symmetric 1-hop neighbors of this
      router.

   o  To find the interface network addresses of the router's symmetric
      2-hop neighbors.

   o  To record this information in Information Bases and thus make this
      information available to other protocols that use this
      neighborhood discovery protocol.

   o  To be available for use by other protocols, which MAY extend the
      information in these Information Bases, including adding new Sets
      to Information Bases, new elements to protocol Tuples and new TLVs
      to be included in outgoing HELLO messages and processed when in
      incoming HELLO messages.

   These objectives are achieved using local (1-hop) signaling that:

   o  Advertises the presence of a router and its interface network
      addresses.

   o  Discovers links from neighboring routers.

   o  Performs bi-directionality checks on the discovered links.

   o  Advertises discovered links, and whether each is symmetric, to its
      1-hop neighbors, and hence discovers symmetric 2-hop neighbors.

   This specification defines, in turn:

   o  Parameters and constants used by the protocol.  Parameters used by
      this protocol may, where appropriate, be specific to a given MANET
      interface or to a MANET router.  This protocol allows all
      parameters to be changed dynamically, and to be set independently
      for each MANET router or MANET interface, as appropriate.




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   o  The Information Bases describing local interfaces, discovered
      links and their status, current and former 1-hop neighbors, and
      symmetric 2-hop neighbors.

   o  The format of the HELLO message that is used for local signaling.

   o  The generation of HELLO messages from some of the information in
      the Information Bases.

   o  The updating of the Information Bases according to received HELLO
      messages and other events.

   o  The response to other events, such as the expiration of
      information in the Information Bases.

4.1.  Routers and Interfaces

   In order for a router to participate in a MANET, it MUST have at
   least one, and possibly more, MANET interfaces.

   Each MANET interface:

   o  Is configured with one or more network addresses.  Each address in
      the range of addresses represented by that network address MUST
      satisfy the following properties:

      o  It MUST be unique to this router, i.e., it MUST NOT be assigned
         to any interface of any other router.

      o  If assigned to other MANET interfaces, on the same router,
         these MANET interfaces MUST be isolated, i.e., addresses may
         only be assigned to different interfaces on the same router if
         no MANET interface on another router can communicate with both.
         For example, interfaces using distinct radio "channels" MAY be
         assigned the same address.

   o  Has a set of interface parameters, defining the behavior of this
      MANET interface.  Each MANET interface MAY be individually
      parameterized.

   o  Has an Interface Information Base, recording information regarding
      links to this MANET interface and symmetric 2-hop neighbors that
      can be reached through such links.

   o  Generates and processes HELLO messages.






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   In addition to a set of MANET interfaces as described above, each
   router has:

   o  A Local Information Base, containing the network addresses of the
      interfaces (MANET and non-MANET) of this router.  The contents of
      this Information Base are not changed by signaling.

   o  A Neighbor Information Base, recording information regarding
      current and recently lost 1-hop neighbors of this router.

   A router may have both MANET interfaces and non-MANET interfaces.
   Interfaces of both of these types are recorded in a router's Local
   Information Base, which is used, but not updated, by the signaling of
   this protocol.

4.2.  Information Base Overview

   Each router maintains protocol state using Information Bases,
   described in the following sections.  Each Information Base consists
   of a number of Protocol Sets.  Each Protocol Set contains a number of
   Protocol Tuples.

   An implementation of this protocol MAY maintain this information in
   the indicated form, or in any other organization that offers access
   to this information.  In particular, note that it is not necessary to
   remove Protocol Tuples from Protocol Sets at the exact time
   indicated, only to behave as if the Protocol Tuples were removed at
   that time.

   Information in the Local Information Base is defined locally and
   included in HELLO messages.  Information in the Interface Information
   Base and the Neighbor Information Base is determined from received
   HELLO messages; some of this information may also be included in
   transmitted HELLO messages.  Such information has a limited duration
   in which it is considered valid.  This duration is determined from
   the VALIDITY_TIME TLV in the HELLO message in which the information
   is received, which in turn is set by the router that originated the
   HELLO message, using its corresponding interface parameter
   H_HOLD_TIME.

   Appendix E illustrates the relationship between message reception,
   included VALIDITY_TIME TLVs, and the duration for which information
   received in a HELLO message is considered valid.  Appendix F
   illustrates some example topologies and how they correspond to
   information in the Information Bases.






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4.2.1.  Local Information Base

   Each router maintains a Local Information Base, which contains the
   router's local configuration information, specifically:

   o  The Local Interface Set, which consists of Local Interface Tuples,
      each of which represents an interface (MANET or non-MANET) of the
      router.

   o  The Removed Interface Address Set, which consists of Removed
      Interface Address Tuples, each of which records a recently used
      network address of an interface (MANET or non-MANET) of the
      router.

   The Local Interface Set is used for generating HELLO messages,
   specifically for determining which interface network addresses are to
   be included and identified as local interfaces.  The Removed
   Interface Address Set is used to avoid incorrectly recording a
   formerly used network address as a symmetric 2-hop neighbor's network
   address.

   The Local Information Base is used for generating signaling, but is
   not itself updated by signaling specified in this document.  Updates
   to the Local Information Base are due to changes of the router
   configuration, and may be allowed to trigger signaling.

4.2.2.  Interface Information Bases

   Each router maintains, for each of its MANET interfaces, an Interface
   Information Base, which contains 1-hop neighborhood and symmetric
   2-hop neighborhood information collected from this MANET interface,
   specifically:

   o  A Link Set, which records information about current and recently
      lost links between this MANET interface and MANET interfaces of
      1-hop neighbors.  The Link Set consists of Link Tuples, each of
      which contains information about a single link.  Link quality
      information (see Section 14), when used, is recorded in Link
      Tuples.

   o  A 2-Hop Set, which records the existence of symmetric links
      between symmetric 1-hop neighbors of this MANET interface and
      other routers (symmetric 2-hop neighbors).  The 2-Hop Set consists
      of 2-Hop Tuples, each of which records a network address of a
      symmetric 2-hop neighbor, and all network addresses of the
      corresponding symmetric 1-hop neighbor.





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   The Link Set for a MANET interface is used for generating HELLO
   messages.  Specifically, the Link Set information is included to both
   allow other routers to identify symmetric links and to populate the
   2-Hop Set.  Recently lost links are recorded in the Link Set for a
   MANET interface so that they can be advertised in HELLO messages,
   accelerating their removal from relevant 1-hop neighbors' Link Sets.

   The Link Set for a MANET interface is itself updated on receiving a
   HELLO message, including recording symmetric links as indicated
   above.  The 2-Hop Set for a MANET interface is updated as indicated
   above, and is not itself used in generating HELLO messages.

4.2.3.  Neighbor Information Base

   Each router maintains a Neighbor Information Base, which contains
   collected information about current and recently lost 1-hop
   neighbors, specifically:

   o  The Neighbor Set consists of Neighbor Tuples, each of which
      records all network addresses of a single 1-hop neighbor.
      Neighbor Tuples are maintained as long as there are corresponding
      Link Tuples.

   o  The Lost Neighbor Set consists of Lost Neighbor Tuples, each of
      which records a network address of a recently lost symmetric 1-hop
      neighbor.

   The Neighbor Set associates all network addresses of each 1-hop
   neighbor.  These network addresses may be included when generating a
   HELLO message, so that other symmetric 1-hop neighbors can record
   this information in a 2-Hop Set.  The Neighbor Set can be updated on
   receiving a HELLO message.

   The Lost Neighbor Set is used to determine which network addresses
   are to be included in a HELLO message as being lost (of a recently
   symmetric 1-hop neighbor).  The Lost Neighbor Set can itself be
   updated on receiving a HELLO message.

4.3.  Signaling Overview

   This protocol contains a signaling mechanism for maintaining the
   Interface Information Bases and the Neighbor Information Base.  If
   information from the link layer, or any other source, is available
   and appropriate, it may also be used to update these Information
   Bases.  Such updates are subject to the constraints specified in
   Appendix B.





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   Signaling consists of a single type of message, known as a HELLO
   message.  Each router generates HELLO messages on each of its MANET
   interfaces.  HELLO messages are generated independently on each MANET
   interface of a MANET router; the content of a given HELLO message
   depends on the MANET interface for which it has been generated.

   Each HELLO message:

   o  Identifies, as far as is required, the MANET interface for which
      it is generated and transmitted; this allows recipients of that
      HELLO message to identify that MANET interface from among those it
      may hear.

   o  Reports the network addresses of other interfaces (MANET and non-
      MANET) of the router; this allows recipients of that HELLO message
      to associate a set of network addresses with a single 1-hop
      neighbor.

   o  Includes 1-hop neighbor information from the Information Bases;
      this allows detection of local symmetric links, and symmetric
      2-hop neighbors.

   HELLO message generation, and the validity of the information
   recorded as a consequence of processing a HELLO message, is affected
   by timers and validity information included in HELLO messages through
   TLVs.  The relationship between message timers and intervals is
   illustrated in Appendix E.

4.3.1.  HELLO Message Generation

   HELLO messages are generated by a router for each of its MANET
   interfaces, and MAY be sent:

   o  Proactively, at a regular interval, known as HELLO_INTERVAL.
      HELLO_INTERVAL may be fixed, or may be dynamic.  For example,
      HELLO_INTERVAL may be backed off due to congestion or network
      stability.

   o  As a response to a change in the router itself, or its 1-hop
      neighborhood, for example, on first becoming active or in response
      to a new, lost, or changed status link.

   o  In a combination of these proactive and responsive mechanisms.

   Jittering of HELLO message generation and transmission SHOULD be used
   as described in Section 11.2, unless the medium access control
   mechanism in use prevents any simultaneous transmissions by
   potentially interfering routers.



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   HELLO messages MAY be scheduled independently for each MANET
   interface, or, interface parameters permitting, using the same
   schedule for all MANET interfaces of a router.

4.3.2.  HELLO Message Content

   The content of a HELLO message MUST satisfy the following:

   o  A HELLO message MUST contain all of the network addresses in the
      Local Interface Set of the router on which the HELLO message is
      being generated.  This includes:

      o  At least one network address of each MANET interface of the
         router.

      o  Network addresses that include all source addresses of any IP
         datagrams sent by the router on any MANET interface.

      o  All other network addresses of the router that are to be made
         known to any other router for any reason.

   o  For each MANET interface, within every time interval equal to the
      corresponding REFRESH_INTERVAL, sent HELLO messages MUST
      collectively include all of the relevant information in the
      corresponding Link Set and the Neighbor Information Base.  Note
      that when determining whether to include information in a HELLO
      message, the sender MUST consider all times up to the latest time
      when it may send its next HELLO message on this MANET interface.

   o  For each MANET interface, within every time interval equal to the
      corresponding REFRESH_INTERVAL, sent HELLO messages MUST
      collectively include all of the relevant information in the
      corresponding Link Set and the Neighbor Information Base.

   o  When determining whether to include a given piece of neighbor
      information in a HELLO message, it is not sufficient to consider
      whether that information has been sent in the interval of length
      REFRESH_INTERVAL up to the current time.  Instead, the router MUST
      consider the interval of length REFRESH_INTERVAL that will end at
      the latest possible time at which the next HELLO message will be
      sent on this MANET interface.  (Normally, this will be
      HELLO_INTERVAL past the current time, but MAY be earlier if this
      router elects to divide its neighbor information among more than
      one HELLO message in order to reduce the size of its HELLO
      messages.)  All neighbor information MUST be sent in this
      interval, i.e., the router MUST ensure that this HELLO message
      includes all neighbor information that has not already been
      included in any HELLO messages sent since the start of this



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      interval (normally, the current time - (REFRESH_INTERVAL -
      HELLO_INTERVAL)).

   o  A HELLO message MUST include exactly one VALIDITY_TIME Message
      TLV, as specified in [RFC5497], that indicates the length of time
      for which the message content is to be considered valid, and is
      therefore to be included in the receiving router's Interface
      Information Base.

   o  A periodically generated HELLO message SHOULD include exactly one
      INTERVAL_TIME Message TLV, as specified in [RFC5497], that
      indicates the current value of HELLO_INTERVAL for that MANET
      interface, i.e., the period within which a further HELLO message
      is guaranteed to be sent on that MANET interface.

4.3.3.  HELLO Message Processing

   HELLO messages received by a router are used to update the Interface
   Information Base for the MANET interface over which that HELLO
   message was received, as well as the Neighbor Information Base of the
   router.  Specifically:

   o  The router ensures that there is a single Neighbor Tuple
      corresponding to the originator of that HELLO message.

   o  The router ensures that there is a Link Tuple, with appropriate
      status (heard or symmetric) and advertised duration, corresponding
      to the link between the MANET interfaces on which that HELLO
      message was sent and received.  One or more Lost Neighbor Tuples
      may be created if the HELLO message reports that the link was
      lost.

   o  If the link between the MANET interfaces on which the HELLO
      message was sent and received is symmetric, then the router
      ensures that there are the appropriate 2-Hop Tuples, with
      advertised duration.

   The processing defined in this specification handles any unexpected
   and erroneous information in a HELLO message, maintaining the
   constraints on Information Base contents specified in Appendix B.

4.4.  Link Quality

   Some links in a MANET may be marginal, e.g., due to adverse wireless
   propagation.  In order to avoid using such marginal links, a link
   quality value is recorded in each Link Tuple.  A MANET router
   considers links for which an insufficient link quality is recorded as
   lost.  Modifying the recorded link quality in a Link Tuple is



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   OPTIONAL.  If link quality is not to be modified, it MUST be set to
   indicate an always usable quality link.

   Note that link quality is a "link admittance" mechanism, allowing a
   router to determine that a given link is too unstable to even
   consider for use.  It is specifically not a link metric nor is it a
   substitute for one.

   Link quality information is only used locally and is not used in
   signaling.  Routers may interoperate whether they are using the same,
   different, or no link quality information.  Link quality information
   is thus not equivalent to a link metric.

   Link quality information is defined in this specification as a
   normalized, dimensionless value in the interval zero to one,
   inclusive, where the greater the value, the better the link quality.
   See Section 14 for further details.

5.  Protocol Parameters and Constants

   The parameters and constants used in this specification are described
   in this section.

5.1.  Protocol and Port Numbers

   This protocol specifies HELLO messages, which are included in packets
   as defined by [RFC5444].  These packets may be sent using either the
   "manet" protocol number or the "manet" well-known UDP port number, as
   specified in [RFC5498].

5.2.  Multicast Address

   This protocol specifies HELLO messages, which are included in packets
   as defined by [RFC5444].  These packets may be locally transmitted
   using the link-local multicast address "LL-MANET-Routers", as
   specified in [RFC5498].

5.3.  Interface Parameters

   The interface parameters used by this specification may be classified
   into the following four categories:

   o  Message intervals

   o  Information validity times

   o  Link quality




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   o  Jitter

   These are detailed in the following sections.

   Different MANET interfaces (on the same or on different routers) MAY
   employ different interface parameter values and MAY change their
   interface parameter values dynamically, subject to the constraints
   given in this section.  A particular case is where all MANET
   interfaces on all MANET routers within a given MANET employ the same
   set of interface parameter values.

5.3.1.  Message Intervals

   HELLO messages serve two principal functions:

   o  To advertise network addresses of this router's interface to its
      1-hop neighbors.  The frequency of these advertisements is
      regulated by the interface parameters HELLO_INTERVAL and
      HELLO_MIN_INTERVAL.

   o  To advertise this router's knowledge of each of its 1-hop
      neighbors.  The frequency of the advertisement of each such
      neighbor is regulated by the interface parameter REFRESH_INTERVAL.

   Specifically, these parameters are as follows:

   HELLO_INTERVAL:
      The maximum time between the transmission of two successive HELLO
      messages on this MANET interface.  If using periodic transmission
      of HELLO messages, these SHOULD be at a separation of
      HELLO_INTERVAL, possibly modified by jitter as specified in
      [RFC5148].

   HELLO_MIN_INTERVAL:
      The minimum interval between transmission of two successive HELLO
      messages on this MANET interface.  (This minimum interval MAY be
      modified by jitter, as defined in [RFC5148].)

   REFRESH_INTERVAL:
      The maximum interval between advertisements, in a HELLO message on
      this MANET interface, of each 1-hop neighbor network address and
      its status.  In all intervals of length REFRESH_INTERVAL, a router
      MUST include each 1-hop neighbor network address and its status in
      at least one HELLO message on this MANET interface.  (This may be
      in the same or in different HELLO messages.)






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   REFRESH_INTERVAL thus represents the frequency at which a piece of
   information, as received in HELLO messages, can be expected to be
   refreshed.  Thus, the REFRESH_INTERVAL is used as a basis for
   determining when such information expires in receiving routers (see
   Section 5.3.2).  HELLO_INTERVAL represents the frequency of HELLO
   message emissions.  Logically, HELLO_INTERVAL cannot be greater than
   the REFRESH_INTERVAL; otherwise, information cannot be refreshed in a
   timely manner.

   HELLO messages can, however, be sent with a higher frequency.  A
   possible use for sending HELLO messages at such a higher frequency
   includes sending partial HELLO messages (e.g., accommodating
   constraints on packet sizes from the underlying medium) refreshing
   only part of the information in each HELLO message.  Another use is
   for a router to send "empty HELLO messages", advertising its own
   presence frequently in smaller HELLO messages (e.g., in case HELLO
   message exchange success rates are used for link quality estimation,
   or to enable rapid detection by new routers in the neighborhood) in
   between HELLO messages refreshing neighbor information in other
   routers.

   The following constraints apply to these interface parameters:

   o  HELLO_INTERVAL > 0

   o  HELLO_MIN_INTERVAL >= 0

   o  HELLO_INTERVAL >= HELLO_MIN_INTERVAL

   o  REFRESH_INTERVAL >= HELLO_INTERVAL

   o  If an INTERVAL_TIME Message TLV as defined in [RFC5497] is
      included in a HELLO message, then HELLO_INTERVAL MUST be
      representable as described in [RFC5497].

   If REFRESH_INTERVAL > HELLO_INTERVAL, then a router may distribute
   its neighbor advertisements between HELLO messages in any manner,
   subject to the constraints above.

   In the absence of any changes to the local neighborhood, a router
   will send a HELLO message on a MANET interface after an (possibly
   jittered) interval of length HELLO_INTERVAL.  For a router to employ
   this protocol in a purely responsive manner on a MANET interface,
   i.e., for the router to only send HELLO messages on that MANET
   interface as a response to external events, HELLO_INTERVAL (and hence
   also REFRESH_INTERVAL) SHOULD be set sufficiently large, i.e., such
   that a responsive HELLO message is always expected with a shorter
   period than this value.



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   If a router has more than one MANET interface, then, even if the
   router configures different values of HELLO_INTERVAL on each MANET
   interface, the router SHOULD configure the same value of
   HELLO_MIN_INTERVAL on all MANET interfaces on which responsive HELLO
   messages may be sent.  (This ensures that changes observed on one
   MANET interface are reported on other MANET interfaces, so that 1-hop
   neighbors connected to the latter can maintain up-to-date 2-hop
   neighborhood information.)

5.3.2.  Information Validity Times

   The following interface parameters manage the validity time of link
   information:

   L_HOLD_TIME:
      The period of advertisement, on this MANET interface, of former
      1-hop neighbor network addresses as lost in HELLO messages,
      allowing recipients of these HELLO messages to accelerate removal
      of this information from their Link Sets.  L_HOLD_TIME MAY be set
      to zero, if accelerated information removal is not required.

   H_HOLD_TIME:
      Used as the Value in the VALIDITY_TIME Message TLV included in all
      HELLO messages on this MANET interface.  It is then used by each
      router receiving such a HELLO message to indicate the validity of
      the information taken from that HELLO message and recorded in the
      receiving router's Information Bases.

   Note that as each item of neighbor information is included in HELLO
   messages within an interval of length REFRESH_INTERVAL, constraints
   on H_HOLD_TIME are based on REFRESH_INTERVAL, not on HELLO_INTERVAL.

   The following constraints apply to these interface parameters:

   o  L_HOLD_TIME >= 0

   o  H_HOLD_TIME >= REFRESH_INTERVAL

   o  If HELLO messages can be lost, then both parameters SHOULD be
      significantly greater than REFRESH_INTERVAL.

   o  H_HOLD_TIME MUST be representable as described in [RFC5497].









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5.3.3.  Link Quality

   The following interface parameters manage the usage of link quality
   (see Section 14):

   HYST_ACCEPT:
      The link quality threshold at or above which a link becomes
      usable, if it was not already so.

   HYST_REJECT:
      The link quality threshold below which a link becomes unusable, if
      it was not already so.

   INITIAL_QUALITY:
      The initial quality of a newly identified link.

   INITIAL_PENDING:
      If true, then a newly identified link is considered pending, and
      is not usable until the link quality has reached or exceeded the
      HYST_ACCEPT threshold.

   The following constraints apply to these interface parameters:

   o  0 <= HYST_REJECT <= HYST_ACCEPT <= 1

   o  0 <= INITIAL_QUALITY <= 1.

   o  If link quality is not updated, then INITIAL_QUALITY >=
      HYST_ACCEPT.

   o  If INITIAL_QUALITY >= HYST_ACCEPT, then INITIAL_PENDING := false.

   o  If INITIAL_QUALITY < HYST_REJECT, then INITIAL_PENDING := true.

5.3.4.  Jitter

   If jitter, as defined in [RFC5148], is used, then these parameters
   are as follows:

   HP_MAXJITTER:
      Represents the value of MAXJITTER used in [RFC5148] for
      periodically generated HELLO messages on this MANET interface.

   HT_MAXJITTER:
      Represents the value of MAXJITTER used in [RFC5148] for externally
      triggered HELLO messages on this MANET interface.

   For constraints on these interface parameters, see [RFC5148].



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5.4.  Router Parameters

   The two router parameters defined by this specification are in the
   category of information validity time.

5.4.1.  Information Validity Time

   The following router parameter manages the validity time of lost
   symmetric 1-hop neighbor information:

   N_HOLD_TIME:
      Used as the period during which former 1-hop neighbor network
      addresses are advertised as lost in HELLO messages, allowing
      recipients of these HELLO messages to accelerate removal of this
      information from their 2-Hop Sets.  N_HOLD_TIME MAY be set to
      zero, if accelerated information removal is not required.

   I_HOLD_TIME:
      The period for which a recently used local interface network
      address is recorded.

   The following constraints apply to these router parameters:

   o  N_HOLD_TIME >= 0

   o  I_HOLD_TIME >= 0

5.5.  Parameter Change Constraints

   If protocol parameters are changed dynamically, the constraints in
   this section apply.

   HELLO_INTERVAL

      o  If the HELLO_INTERVAL for a MANET interface increases, then the
         next HELLO message on this MANET interface MUST be generated
         according to the previous, shorter, HELLO_INTERVAL.  A number
         of subsequent HELLO messages MAY be generated according to the
         previous, shorter, HELLO_INTERVAL (but MUST include times
         according to current parameters).  This ensures that "promises"
         as to timely transmission of a future HELLO message are kept
         until these previous promises have expired.

      o  If the HELLO_INTERVAL for a MANET interface decreases, then the
         following HELLO messages on this MANET interface MUST be
         generated according to this current, shorter, HELLO_INTERVAL.





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   REFRESH_INTERVAL

      o  If the REFRESH_INTERVAL for a MANET interface increases, then
         the content of subsequent HELLO messages must be organized such
         that the specification of the old value of REFRESH_INTERVAL is
         satisfied for a further period equal to the old value of
         REFRESH_INTERVAL.

      o  If the REFRESH_INTERVAL for a MANET interface decreases, then
         it MAY be necessary to reschedule HELLO message generation on
         that MANET interface, in order for the specification of
         REFRESH_INTERVAL is satisfied from the time of change.

   HYST_ACCEPT and HYST_REJECT

      o  If HYST_ACCEPT or HYST_REJECT changes, then the appropriate
         actions for link quality change, as specified in Section 14.3,
         MUST be taken.

   L_HOLD_TIME

      o  If L_HOLD_TIME changes, then the expiry times of all relevant
         Link Tuples MUST be changed.

   N_HOLD_TIME

      o  If N_HOLD_TIME changes, then the expiry times of all relevant
         Lost Neighbor Tuples MUST be changed.

   HP_MAXJITTER

      o  If HP_MAXJITTER changes, then the periodic HELLO message
         schedule on this MANET interface MAY be changed.

   HT_MAXJITTER

      o  If HT_MAXJITTER changes, then externally triggered HELLO
         messages on this MANET interface MAY be rescheduled.

5.6.  Constants

   The constant C (time granularity) is used as specified in [RFC5497].

6.  Local Information Base

   A router maintains a Local Information Base that records information
   about its interfaces (MANET and non-MANET).  Each interface of a
   router MUST be identified by at least one network address.  Such



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   network addresses MAY be specific to that interface, or MAY in some
   circumstances be used by more than one interface as specified below.

   The Local Information Base is not modified by signaling.  If a
   router's interface configuration changes, then the Local Information
   Base MUST reflect these changes.  This MAY also result in signaling
   to advertise these changes.

   It is not necessary to include all addresses of an interface in the
   Local Information Base, and hence in HELLO messages.  However, any
   address that may be the source address of an IP datagram sent from
   that interface MUST be included (and at least one address MUST be
   included).  A protocol using this specification MAY add additional
   requirements to these, e.g., that any address that may be the
   destination address of an IP datagram is also included.

   The addresses assigned to an interface are "owned" by the router, and
   MUST NOT be used by any other router as an interface address.  If an
   address has a prefix length and represents a range of addresses, this
   applies to all addresses in that range (i.e., such ranges MUST NOT
   overlap).

   The addresses assigned to different interfaces on the same router
   MUST be distinct (hence, network address ranges MUST NOT overlap)
   except that:

   o  The same address MAY be assigned to any number of non-MANET
      interfaces as well as to one (or more if the following condition
      also applies) MANET interface.

   o  The same address MAY be assigned to two (or more if each pair
      satisfies this condition) MANET interfaces if those two MANET
      interfaces cannot communicate to, from, or one to and one from any
      other MANET interface of another router.

6.1.  Local Interface Set

   A router's Local Interface Set records its local interfaces.  It
   consists of Local Interface Tuples, one per interface:

      (I_local_iface_addr_list, I_manet)

   where:

      I_local_iface_addr_list is an unordered list of the network
      addresses of this interface.





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      I_manet is a boolean flag, describing if this interface is a MANET
      interface.

   Local Interface Tuples are removed from the Local Interface Set only
   when the routers' interface configuration changes, subject to
   Section 9, i.e., they are not subject to timer-based expiration.

6.2.  Removed Interface Address Set

   A router's Removed Interface Address Set records network addresses
   that were recently used as local interface network addresses.  If a
   router's interface network addresses are immutable, then the Removed
   Interface Address Set is always empty and MAY be omitted.  It
   consists of Removed Interface Address Tuples, one per network
   address:

      (IR_local_iface_addr, IR_time)

   where:

      IR_local_iface_addr is a recently used network address of an
      interface of this router.

      IR_time specifies when this Tuple expires and MUST be removed.

7.  Interface Information Bases

   A router maintains an Interface Information Base for each of its
   MANET interfaces.  This records information about links to that MANET
   interface and symmetric 2-hop neighbors that can be reached in two
   hops using those links as the first hop.  Each Interface Information
   Base includes a Link Set and a 2-Hop Set.

   A network address of a symmetric 2-hop neighbor can also be present
   as the network address of a 1-hop neighbor.  This allows the router
   using this network address to be immediately considered as a
   symmetric 2-hop neighbor if it fails to be a symmetric 1-hop
   neighbor.

   An element that specifies a time is considered expired if the current
   time is greater than or equal to that time.  One such element,
   present in most Tuples, indicates, when expired, that the Tuple
   itself is considered expired and MUST be removed.  Tuples that do not
   have such a time element are removed at other times as specified; for
   example, a Neighbor Tuple is removed when all corresponding Link
   Tuples have been removed.





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7.1.  Link Set

   An interface's Link Set records links from other routers that are, or
   recently were, 1-hop neighbors.  It consists of Link Tuples, each
   representing a single link:

      (L_neighbor_iface_addr_list, L_HEARD_time, L_SYM_time,
       L_quality, L_pending, L_lost, L_time)

   where:

      L_neighbor_iface_addr_list is an unordered list of the network
      addresses of the MANET interface of the 1-hop neighbor;

      L_HEARD_time is the time up to which the MANET interface of the
      1-hop neighbor would be considered heard if not considering link
      quality;

      L_SYM_time is the time up to which the link to the 1-hop neighbor
      would be considered symmetric if not considering link quality;

      L_quality is a dimensionless number between 0 (inclusive) and 1
      (inclusive) describing the quality of a link; a greater value of
      L_quality indicating a higher quality link;

      L_pending is a boolean flag, describing if a link is considered
      pending (i.e., a candidate, but not yet established, link);

      L_lost is a boolean flag, describing if a link is considered lost
      due to low link quality;

      L_time specifies when this Tuple expires and MUST be removed.

   The status of the link, as obtained through HELLO message exchange
   and using link quality, is denoted L_status.  L_status can take the
   Values PENDING, HEARD, SYMMETRIC, and LOST.  The values LOST,
   SYMMETRIC, and HEARD are defined in Section 18.5.  The Value PENDING
   is never used in a HELLO message, it is only used locally by a
   router, and any Value distinct from LOST, SYMMETRIC, and HEARD may be
   used.

   L_status is defined by:

   1.  If L_pending = true, then L_status := PENDING;

   2.  otherwise, if L_lost = true, then L_status := LOST;





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   3.  otherwise, if L_SYM_time is not expired, then L_status :=
       SYMMETRIC;

   4.  otherwise, if L_HEARD_time is not expired, then L_status :=
       HEARD;

   5.  otherwise, L_status := LOST.

7.2.  2-Hop Set

   An interface's 2-Hop Set records network addresses of symmetric 2-hop
   neighbors, and the symmetric links to symmetric 1-hop neighbors
   through which these symmetric 2-hop neighbors can be reached.  It
   consists of 2-Hop Tuples, each representing a single network address
   of a symmetric 2-hop neighbor, and a single MANET interface of a
   symmetric 1-hop neighbor.

      (N2_neighbor_iface_addr_list, N2_2hop_addr, N2_time)

   where:

      N2_neighbor_iface_addr_list is an unordered list of the network
      addresses of the MANET interface of the symmetric 1-hop neighbor
      from which this information was received;

      N2_2hop_addr is a network address of a symmetric 2-hop neighbor
      that has a symmetric link (using any MANET interface) to the
      indicated symmetric 1-hop neighbor;

      N2_time specifies when this Tuple expires and MUST be removed.

8.  Neighbor Information Base

   Each router maintains a Neighbor Information Base that records
   information about network addresses of current and recently symmetric
   1-hop neighbors.

8.1.  Neighbor Set

   A router's Neighbor Set records all network addresses of each 1-hop
   neighbor.  It consists of Neighbor Tuples, each representing a single
   1-hop neighbor:

      (N_neighbor_addr_list, N_symmetric)







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   where:

      N_neighbor_addr_list is an unordered list of the network addresses
      of a 1-hop neighbor;

      N_symmetric is a boolean flag, describing if this is a symmetric
      1-hop neighbor.

   Neighbor Tuples are removed from the Neighbor Set only when
   corresponding Link Tuples expire from the routers' Link Set, i.e.,
   Neighbor Tuples are not directly subject to timer-based expiration.

8.2.  Lost Neighbor Set

   A router's Lost Neighbor Set records network addresses of routers
   that recently were symmetric 1-hop neighbors but that are now
   advertised as lost.  It consists of Lost Neighbor Tuples, each
   representing a single such network address:

      (NL_neighbor_addr, NL_time)

   where:

      NL_neighbor_addr is a network address of a router that recently
      was a symmetric 1-hop neighbor of this router;

      NL_time specifies when this Tuple expires and MUST be removed.

9.  Local Information Base Changes

   The Local Information Base MUST be updated in response to changes in
   the router's local interface configuration.  These MAY also change
   the Interface Information Base and the Neighbor Information Base.  If
   any changes to the latter Information Bases satisfy any of the
   conditions described in Section 13, then those changes MUST be
   applied immediately, unless noted otherwise below.

   A router MAY transmit HELLO messages in response to these changes.

9.1.  Adding an Interface

   If an interface is added to the router, then this is indicated by the
   addition of a Local Interface Tuple to the Local Interface Set.  If
   the new interface is a MANET interface, then an initially empty
   Interface Information Base MUST be created for this new MANET
   interface.  The actions in Section 9.3 MUST be taken for each network
   address of this added interface.  A HELLO message MAY be sent on all
   MANET interfaces, it SHOULD be sent on the new interface if it is a



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   MANET interface.  If using scheduled messages, then a message
   schedule MUST be established on the new MANET interface.

9.2.  Removing an Interface

   If an interface is removed from the router, then this MUST result in
   changes to the Local Information Base and to the Neighbor Information
   Base as follows:

   1.  Identify the Local Interface Tuple that corresponds to the
       interface to be removed.

   2.  For each network address (henceforth removed address) in the
       I_local_iface_addr_list of that Local Interface Tuple, if that
       network address is not in the I_local_iface_addr_list of any
       other Local Interface Tuple, then create a Removed Interface
       Address Tuple with:

       o  IR_local_iface_addr := removed address;

       o  IR_time := current time + I_HOLD_TIME.

   3.  Remove that Local Interface Tuple from the Local Interface Set.

   4.  If the interface to be removed is a MANET interface (i.e., with
       I_manet = true), then:

       1.  Remove the Interface Information Base for that MANET
           interface;

       2.  All Neighbor Tuples for which none of the network addresses
           in its N_neighbor_addr_list are contained in any
           L_neighbor_iface_addr_list in any remaining Link Tuple are
           removed.

   If the removed interface is the last MANET interface of the router,
   then there will be no remaining Interface Information Bases, and the
   router will no longer participate in this protocol.

   After removing the interface and making these changes, a HELLO
   message MAY be sent on all remaining MANET interfaces.

9.3.  Adding a Network Address to an Interface

   If a network address is added to an interface, then this is indicated
   by the addition of a network address to the appropriate
   I_local_iface_addr_list.  The following changes MUST be made to the
   Information Bases:



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   1.  Remove any Removed Interface Address Tuple whose
       IR_local_iface_addr is the added network address.

   2.  Remove any Neighbor Tuples whose N_neighbor_addr_list contains a
       network address that overlaps the added network address.

   3.  Remove any Link Tuples, in any Link Set, for which either:

       o  L_neighbor_iface_addr_list contains any network address in the
          N_neighbor_addr_list of any removed Neighbor Tuple; OR

       o  L_neighbor_iface_addr_list contains a network address that
          overlaps the added network address.

       Apply Section 13.2 but not Section 13.3.

   4.  Remove any Lost Neighbor Tuples whose NL_neighbor_addr overlaps
       the added network address.

   5.  Remove any 2-Hop Tuples whose N2_2hop_addr overlaps the added
       network address.

   After adding the network address and making these changes, a HELLO
   message MAY be sent on all MANET interfaces.

   These changes, other than to the appropriate I_local_iface_addr_list,
   are made in order to maintain consistency of the Information Bases.
   Specifically, these changes remove any record of any use of this
   network address by routers in the 1-hop neighborhood or in the
   symmetric 2-hop neighborhood of this router.

9.4.  Removing a Network Address from an Interface

   If a network address (henceforth removed address) is removed from an
   interface, then:

   1.  Identify the Local Interface Tuple that corresponds to the
       removed address.

   2.  If this is the only network address of that interface (the only
       network address in the corresponding I_local_iface_addr_list),
       then remove that interface as specified in Section 9.2.

   3.  Otherwise:

       1.  Remove the removed address from this I_local_iface_addr_list.





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       2.  If the removed address is not in the I_local_iface_addr_list
           of any other Local Interface Tuple, then create a Removed
           Interface Address Tuple with:

           o  IR_local_iface_addr := removed address;

           o  IR_time := current time + I_HOLD_TIME.

   After removing the network address and making these changes, a HELLO
   message MAY be sent on all MANET interfaces.

10.  Packets and Messages

   The packet and message format used by this protocol is defined in
   [RFC5444], which is used with the following considerations:

   o  This protocol specifies one Message Type, the HELLO message.

   o  A HELLO message MAY use any combination of Message Header options
      specified in [RFC5444].

   o  HELLO messages MUST NOT be forwarded, i.e., a <msg-hop-limit>, if
      present, MUST have the value 1.

   o  HELLO messages MAY be included in multi-message packets as
      specified in [RFC5444].

   o  Received HELLO messages MUST be parsed in accordance with
      [RFC5444].  A HELLO message that is not in conformance with
      [RFC5444] MUST be discarded without being processed.  A HELLO
      message can also be discarded without being processed for other
      reasons, see Section 12.1.

   o  This protocol specifies three Address Block TLVs.  It also uses
      two Message TLVs defined in [RFC5497].  These five TLV Types are
      all defined only with Type Extension = 0.  TLVs of other types,
      and of these types but without Type Extension = 0, are ignored by
      this protocol.  All references in this specification to, for
      example, an Address Block TLV with Type = LINK_STATUS, are to be
      considered as referring to an Address Block TLV with Type =
      LINK_STATUS and Type Extension = 0.

10.1.  HELLO Messages

   A HELLO message MUST contain:

   o  Exactly one VALIDITY_TIME Message TLV as specified in [RFC5497],
      representing H_HOLD_TIME for the transmitting MANET interface.



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      The options included in [RFC5497] for representing zero and
      infinite times MUST NOT be used.

   A HELLO message transmitted due to a periodic timer SHOULD contain,
   and otherwise (i.e., transmitted for any other reason, in particular
   in response to any Information Base changes) MAY contain:

   o  Exactly one INTERVAL_TIME Message TLV as specified in [RFC5497],
      representing HELLO_INTERVAL for the transmitting MANET interface.
      The options included in [RFC5497] for representing zero and
      infinite times MUST NOT be used.

   A HELLO message MAY contain:

   o  Other Message TLVs.

   o  One or more Address Blocks, each with an associated Address Block
      TLV Block, which MAY contain other Address Block TLVs.

10.1.1.  Address Blocks

   All network addresses in a router's Local Interface Set (i.e., in any
   I_local_iface_addr_list) MUST be represented as address objects (see
   [RFC5444]), and included in the Address Blocks in all generated HELLO
   messages, with the following permitted exception:

   o  If the MANET interface on which the HELLO message is to be sent
      has a single address with maximum prefix length (i.e., /32 for
      IPv4, /128 for IPv6), then that address MAY be omitted from being
      included in any Address Block, provided that this address is
      included as the sending address of the IP datagram in which the
      HELLO message is included.

   All network addresses of the router's interfaces included in any
   Address Block(s) MUST be associated with an Address Block TLV with
   Type = LOCAL_IF, as defined in Table 1.

   +----------+---------+----------------------------------------------+
   |   Name   |  Value  | Description                                  |
   |          |  Length |                                              |
   +----------+---------+----------------------------------------------+
   | LOCAL_IF | 1 octet | Specifies that the network address is        |
   |          |         | associated with the MANET interface on which |
   |          |         | the message was sent (THIS_IF) or another    |
   |          |         | interface of the sending router (OTHER_IF).  |
   +----------+---------+----------------------------------------------+

                     Table 1: LOCAL_IF TLV Definition



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   Address Blocks MAY contain current or recently lost 1-hop neighbors'
   network addresses, represented as address objects (see [RFC5444]),
   each of which is associated with one or both Address Block TLVs as
   described in Table 2.

   +--------------+---------+------------------------------------------+
   |     Name     |  Value  | Description                              |
   |              |  Length |                                          |
   +--------------+---------+------------------------------------------+
   |  LINK_STATUS | 1 octet | Specifies the status of the link from    |
   |              |         | the indicated network address and to the |
   |              |         | MANET interface over which the HELLO     |
   |              |         | message is transmitted (LOST, SYMMETRIC, |
   |              |         | or HEARD).                               |
   | OTHER_NEIGHB | 1 octet | Specifies that the network address is    |
   |              |         | (SYMMETRIC) or was (LOST) of a MANET     |
   |              |         | interface of a symmetric 1-hop neighbor  |
   |              |         | of the router transmitting the HELLO     |
   |              |         | message.                                 |
   +--------------+---------+------------------------------------------+

           Table 2: LINK_STATUS and OTHER_NEIGHB TLV Definition

   An Address Block TLV with Type = LINK_STATUS and Value = SYMMETRIC or
   Value = LOST also performs the function of an Address Block TLV with
   Type = OTHER_NEIGHB and the same Value.  Including the latter
   associated with the same address object is discouraged for efficiency
   reasons.  If an Address Block TLV with Type = LINK_STATUS and Value =
   SYMMETRIC is combined with an Address Block TLV with Type =
   OTHER_NEIGHB and Value = LOST associated with the same address
   object, then the latter MUST be ignored and SHOULD NOT be included.
   See Appendix A.

   Other network addresses MAY be represented as address objects (see
   [RFC5444]) and included in Address Blocks, but MUST NOT be associated
   with any of the Address Block TLVs specified in this specification.

11.  HELLO Message Generation

   Each MANET interface MUST generate HELLO messages according to the
   specification in this section.  HELLO messages are generated for each
   MANET interface independently.  HELLO message generation and
   scheduling MUST be according to the interface parameters for that
   MANET interface, and MAY be independent for each MANET interface or,
   interface parameters permitting, MANET interfaces MAY use the same
   schedule.





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   If transmitting periodic HELLO messages, then, following a HELLO
   message transmission on a MANET interface, another HELLO message MUST
   be transmitted on the same MANET interface after an interval not
   greater than HELLO_INTERVAL.  Two successive HELLO message
   transmissions on the same MANET interface MUST be separated by at
   least HELLO_MIN_INTERVAL, except as noted in Section 11.2.1.

11.1.  HELLO Message Specification

   HELLO messages are generated independently on each MANET interface.

   All network addresses in any I_local_iface_addr_list MUST be
   included, represented as address objects (see [RFC5444]), except
   that:

   o  If the interface on which the HELLO message is to be sent has a
      single address with maximum prefix length (i.e., /32 for IPv4,
      /128 for IPv6), then that address MAY be omitted, provided that
      this address is included as the sending address of the IP datagram
      in which the HELLO message is included.

   All such included address objects MUST be associated with an Address
   Block TLV with Type := LOCAL_IF and Value according to the following:

   o  If the address object represents a network address of the sending
      MANET interface, then Value := THIS_IF.

   o  Otherwise, Value := OTHER_IF.

   If such a network address is included in more than one
   I_local_iface_addr_list, then, for efficiency reasons, it is
   encouraged that the corresponding address object is associated with
   only one Value using an Address Block TLV with Type := LOCAL_IF; this
   MUST be Value := THIS_IF if the address object represents a network
   address of the sending MANET interface.

   The following network addresses of current or former 1-hop neighbors
   MAY be represented as address objects (see [RFC5444]) and included in
   any HELLO message, respecting the parameter REFRESH_INTERVAL for each
   association for that MANET interface, and according to the following:

   o  Network addresses of MANET interfaces of 1-hop neighbors from the
      Link Set of the Interface Information Base for this MANET
      interface (i.e., from an L_neighbor_iface_addr_list), other than
      those from Link Tuples with L_status = PENDING.






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   o  Other network addresses of symmetric 1-hop neighbors from the
      Neighbor Set of this router's Neighbor Information Base (i.e.,
      from an N_neighbor_addr_list).

   o  Network addresses of MANET interfaces of previously symmetric or
      heard 1-hop neighbors connected on this MANET interface from the
      Link Set of the Interface Information Base for this MANET
      interface (i.e., from an L_neighbor_iface_addr_list with L_status
      = LOST).

   o  Other network addresses of previously symmetric 1-hop neighbors
      from the Lost Neighbor Set of this router's Neighbor Information
      Base (i.e., from an NL_neighbor_addr).

   Each such address object (see [RFC5444]) MUST be associated with one
   or more appropriate Address Block TLVs.  Specifically:

   1.  For each address object (henceforth linked address) that
       represents a network address contained in an
       L_neighbor_iface_addr_list of a Link Tuple in the Link Set for
       this MANET interface, for which L_status != PENDING, include the
       linked address with an associated Address Block TLV with:

       o  Type := LINK_STATUS; AND

       o  Value := L_status.

   2.  For each address object (henceforth neighbor address) that
       represents a network address contained in an N_neighbor_addr_list
       in a Neighbor Tuple with N_symmetric = true and that has not
       already been included with an associated Address Block TLV with
       Type = LINK_STATUS and Value = SYMMETRIC, include the neighbor
       network address with an associated Address Block TLV with:

       o  Type := OTHER_NEIGHB; AND

       o  Value := SYMMETRIC.

   3.  For each Lost Neighbor Tuple whose NL_neighbor_addr (henceforth
       lost address) has not already been represented as an address
       object and included, include lost address with an associated
       Address Block TLV with:

       o  Type := OTHER_NEIGHB; AND

       o  Value := LOST.





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   If any such network addresses have been added to these Information
   Bases since the last HELLO message was sent on this MANET interface,
   or if their status (as indicated by these TLVs and the Values they
   associate with that network address) have changed since that network
   address was last reported on this MANET interface, then that network
   address, and the indicated TLVs, SHOULD be included in the HELLO
   message.

   If the address object (see [RFC5444]) representing a network address
   of a 1-hop neighbor is specified with more than one associated
   Address Block TLV, then these Address Block TLVs MAY be independently
   included or excluded from each HELLO message.  Each such Address
   Block TLV MUST be included associated with the address object
   representation of that network address in a HELLO message sent on
   that MANET interface in every interval of length equal to that MANET
   interface's parameter REFRESH_INTERVAL.  Address Block TLVs
   associated with the same address object included in the same HELLO
   message MAY be applied to the same or different copies of that
   address object.

   An implementation of this protocol MAY limit the information included
   in each HELLO message, for example, to accommodate smaller MTU sizes.
   HELLO messages remain constrained by the above requirements, in
   particular, that all local interface information MUST be included in
   all HELLO messages, and that all neighbor information MUST be sent
   within each interval of length REFRESH_INTERVAL.  This neighbor
   information MAY, however, be sent in the same or in different HELLO
   messages.

11.2.  HELLO Message Transmission

   HELLO messages are transmitted in the format specified by [RFC5444].

11.2.1.  HELLO Message Jitter

   HELLO messages MAY be sent using periodic message generation or
   externally triggered message generation.  If using data link and
   physical layers that are subject to packet loss due to collisions,
   HELLO messages SHOULD be jittered as described in [RFC5148].

   Internally triggered message generation (such as due to a change in
   local interfaces) MAY be treated as if externally generated message
   generation or MAY be not jittered.

   HELLO messages MUST NOT be forwarded, and thus message forwarding
   jitter does not apply to HELLO messages.





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   Each form of jitter described in [RFC5148] requires a parameter
   MAXJITTER.  These interface parameters may be dynamic and are
   specified by:

   o  For periodic message generation: HP_MAXJITTER.

   o  For externally triggered message generation: HT_MAXJITTER.

   When HELLO message generation is delayed in order that a HELLO
   message is not sent within HELLO_MIN_INTERVAL of the previous HELLO
   message on the same MANET interface, then HELLO_MIN_INTERVAL SHOULD
   be reduced by jitter, with maximum reduction HP_MAXJITTER, as
   described in [RFC5148].  In this case, HP_MAXJITTER MUST NOT be
   greater than HELLO_MIN_INTERVAL.

12.  HELLO Message Processing

   On receiving a HELLO message, a router MUST first check if the
   message is invalid for processing by this router, as defined in
   Section 12.1 and, if so, discard the message without further
   processing.  Otherwise, for each received and valid HELLO message,
   the receiving router MUST update its appropriate Interface
   Information Base and its Neighbor Information Base as specified in
   Section 12.3 to Section 12.6.  These updates MUST be performed in the
   order in which they are presented in this specification.  If any
   changes satisfy any of the conditions described in Section 13, then
   the indicated consequences in that section MUST be applied
   immediately, unless noted otherwise.

   All message processing, including determination of whether a message
   is invalid, considers only TLVs with Type Extension = 0.  TLVs with
   any other type extension are ignored.  All references to, for
   example, a TLV with Type = LINK_STATUS refer to a TLV with Type =
   LINK_STATUS and Type Extension = 0.

12.1.  Invalid Message

   A received HELLO message is invalid for processing by this router if
   any of the following conditions are true:

   o  The address length as specified in the Message Header is not equal
      to the length of the addresses used by this router.

   o  The message has a <msg-hop-limit> field in its Message Header with
      a value other than one.  (Note that the message does not need to
      have a <msg-hop-limit> field.)





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   o  The message has a <msg-hop-count> field in its Message Header with
      a value other than zero.  (Note that the message does not need to
      have a <msg-hop-count> field.)

   o  The message does not have a Message TLV with Type = VALIDITY_TIME
      in its Message TLV Block.

   o  The message has more than one Message TLV with Type =
      VALIDITY_TIME in its Message TLV Block.

   o  The message has more than one Message TLV with Type =
      INTERVAL_TIME in its Message TLV Block.

   o  The message has any Address Block TLV(s) with Type = LOCAL_IF and
      any single Value v such that v != THIS_IF and v != OTHER_IF.

   o  Any address object (including different address objects
      representing the same network address, in the same or different
      Address Blocks) is associated with more than one Value by one or
      more Address Block TLV(s) with Type = LOCAL_IF.

   o  Any address object (henceforth local address) associated with an
      Address Block TLV with Type = LOCAL_IF represents one of the
      receiving router's current or recently used network addresses
      (i.e., local address overlaps any network address in any
      I_local_iface_addr_list in the Local Interface Set or any
      IR_local_iface_addr in the Removed Interface Address Set).

   o  The message has any Address Block TLV(s) with Type = LINK_STATUS
      with any single Value v such that v != LOST, v != SYMMETRIC, and v
      != HEARD.

   o  The message has any Address Block TLV(s) with Type = OTHER_NEIGHB
      with any single Value v such that v != LOST and v != SYMMETRIC.

   o  Any address object (including different copies of an address
      object, in the same or different Address Blocks) is associated
      with an Address Block TLV with Type = LOCAL_IF and with an Address
      Block TLV with Type = LINK_STATUS.

   o  Any address object (including different copies of an address
      object, in the same or different Address Blocks) is associated
      with an Address Block TLV with Type = LOCAL_IF and with an Address
      Block TLV with Type = OTHER_NEIGHB.







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   o  Any address object (including different copies of an address
      object, in the same or different Address Blocks) is associated
      with more than one Value by one or more Address Block TLVs with
      Type = LINK_STATUS.

   o  Any address object (including different copies of an address
      object, in the same or different Address Blocks) is associated
      with more than one Value by one or more Address Block TLVs with
      Type = OTHER_NEIGHB.

   A router MAY recognize additional reasons for identifying that a
   message is badly formed and therefore invalid for processing, e.g.,
   to allow a security protocol as suggested in Section 17 to perform
   verification of HELLO message signatures and prevent processing of
   unverifiable HELLO messages by this protocol.

   An invalid message MUST be silently discarded, without updating the
   router's Information Bases.

12.2.  Definitions

   For the purpose of this section, note the following definitions:

   o  "validity time" is calculated from the Message TLV with Type =
      VALIDITY_TIME of the HELLO message as specified in [RFC5497].
      (Note that, as specified by Section 12.1, there must be exactly
      one such Message TLV in the HELLO message.)  All information in
      the HELLO message used by this specification has the same validity
      time.

   o  "Receiving Address List" is the I_local_iface_addr_list
      corresponding to the MANET interface on which the HELLO message
      was received

   o  "Sending Address List" is an unordered list of network addresses
      of the MANET interface over which the HELLO message was sent,
      i.e., is an unordered list of the network addresses represented by
      address objects contained in the HELLO message with an associated
      Address Block TLV with Type = LOCAL_IF and Value = THIS_IF.  If
      the Sending Address List is otherwise empty, then the Sending
      Address List contains a single network address with maximum prefix
      length (i.e., /32 for IPv4, /128 for IPv6) with an address equal
      to the sending address of the IP datagram in which the HELLO
      message was included.

   o  "Neighbor Address List" is an unordered list of all the network
      addresses of all the interfaces of the router that generated the
      HELLO message, i.e., is the Sending Address List, plus the network



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      addresses represented by address objects contained in the HELLO
      message with an associated Address Block TLV with Type = LOCAL_IF
      and Value = OTHER_IF.

   o  "EXPIRED" indicates that a timer is set to a value clearly
      preceding the current time (e.g., current time - 1).

   o  "Removed Address List" is a list of network addresses created by
      this HELLO message processing that were formerly reported as local
      by the router originating the HELLO message but that are not
      included in the Neighbor Address List.  This list is initialized
      as empty.

   o  "Lost Address List" is a subset of the Removed Address List
      containing network addresses that were formerly considered as
      symmetric.  This list is initialized as empty.

12.3.  Updating the Neighbor Set

   On receiving a HELLO message, the router MUST update its Neighbor Set
   and populate the Removed Address List and Lost Address List:

   1.  Find all Neighbor Tuples (henceforth matching Neighbor Tuples)
       where N_neighbor_addr_list contains any network address that
       overlaps with any network address in the Neighbor Address List.

   2.  If there are no matching Neighbor Tuples, then:

       1.  Create a new Neighbor Tuple with:

           o  N_neighbor_addr_list := Neighbor Address List;

           o  N_symmetric := false.

   3.  If there is one matching Neighbor Tuple, then:

       1.  If the matching Neighbor Tuple's N_neighbor_addr_list !=
           Neighbor Address List, then:

           1.  For each network address (henceforth removed address)
               that is contained in that N_neighbor_addr_list but that
               is not contained in the Neighbor Address List:

               1.  Add the removed address to the Removed Address List.

               2.  If N_symmetric = true, then add the removed address
                   to the Lost Address List.




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           2.  Update the matching Neighbor Tuple by:

               o  N_neighbor_addr_list := Neighbor Address List.

   4.  If there are two or more matching Neighbor Tuples, then:

       1.  For each network address (henceforth removed address) that is
           contained in the N_neighbor_addr_list of any of the matching
           Neighbor Tuples but is not contained in the Neighbor Address
           List:

           1.  Add removed address to the Removed Address List.

           2.  If N_symmetric = true, then add removed address to the
               Lost Address List.

       2.  Replace the matching Neighbor Tuples by a single Neighbor
           Tuple with:

           o  N_neighbor_addr_list := Neighbor Address List;

           o  N_symmetric := false

12.4.  Updating the Lost Neighbor Set

   On receiving a HELLO message, a router MUST update its Lost Neighbor
   Set:

   1.  For each network address (henceforth lost address) that is
       contained in the Lost Address List, if no Lost Neighbor Tuple
       with NL_neighbor_addr = lost address exists, then add a Lost
       Neighbor Tuple with:

       o  NL_neighbor_addr := lost address;

       o  NL_time := current time + N_HOLD_TIME.

12.5.  Updating the Link Sets

   On receiving a HELLO message, a router MUST update its Link Sets:

   1.  Remove all network addresses in the Removed Address List from the
       L_neighbor_iface_addr_list of all Link Tuples.

   2.  Remove all Link Tuples whose L_neighbor_iface_addr_list is now
       empty; apply Section 13.2 but not Section 13.3.





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   The router MUST then update its Link Set for the MANET interface on
   which the HELLO message is received:

   1.  Find all Link Tuples (henceforth matching Link Tuples) where:

       o  L_neighbor_iface_addr_list contains one or more network
          addresses in the Sending Address List.

   2.  If there is more than one matching Link Tuple, then remove them
       all; apply Section 13.2 but not Section 13.3.

   3.  If no matching Link Tuples remain, then create a new matching
       Link Tuple with:

       o  L_neighbor_iface_addr_list := empty;

       o  L_HEARD_time := EXPIRED;

       o  L_SYM_time := EXPIRED;

       o  L_quality := INITIAL_QUALITY;

       o  L_pending := INITIAL_PENDING;

       o  L_lost := false;

       o  L_time := current time + validity time.

   4.  The matching Link Tuple, existing or new, is then modified as
       follows:

       1.  If the router finds any network address (henceforth receiving
           address) in the Receiving Address List in an Address Block in
           the HELLO message, then the Link Tuple is modified as
           follows:

           1.  If any receiving address in the HELLO message is
               associated with an Address Block TLV with Type =
               LINK_STATUS and with Value = HEARD or Value = SYMMETRIC,
               then:

               o  L_SYM_time := current time + validity time.

           2.  Otherwise, if any receiving address in the HELLO message
               is associated with an Address Block TLV with Type =
               LINK_STATUS and Value = LOST, then:

               1.  if L_SYM_time has not expired, then:



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                   1.  L_SYM_time := EXPIRED.

                   2.  if L_status = HEARD, then:

                       o  L_time := current time + L_HOLD_TIME.

       2.  L_neighbor_iface_addr_list := Sending Address List.

       3.  L_HEARD_time := max(current time + validity time,
           L_SYM_time).

       4.  If L_status = PENDING, then:

           o  L_time := max(L_time, L_HEARD_time).

       5.  Otherwise, if L_status = HEARD or L_status = SYMMETRIC, then:

           o  L_time := max(L_time, L_HEARD_time + L_HOLD_TIME).

12.6.  Updating the 2-Hop Set

   On receiving a HELLO message, a router MUST update its 2-Hop Set for
   the MANET interface on which the HELLO message was received:

   1.  Remove all network addresses in the Removed Address List from the
       N2_neighbor_iface_addr_list of all 2-Hop Tuples.

   2.  If the Link Tuple whose L_neighbor_iface_addr_list = Sending
       Address List, has L_status = SYMMETRIC, then:

       1.  For each network address (henceforth 2-hop address) in an
           Address Block of the HELLO message, where:

           o  a 2-hop address is not contained in the Neighbor Address
              List;

           o  a 2-hop address is not contained in any
              I_local_iface_addr_list; AND

           o  a 2-hop address != any IR_local_iface_addr

           perform the following processing:

           1.  If the 2-hop address has an associated Address Block TLV
               with:

               o  Type = LINK_STATUS and Value = SYMMETRIC; OR




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               o  Type = OTHER_NEIGHB and Value = SYMMETRIC,

               then, if there is no 2-Hop Tuple such that:

               o  N2_neighbor_iface_addr_list contains one or more
                  network addresses in the Sending Address List; AND

               o  N2_2hop_addr = 2-hop address,

               then create a 2-Hop Neighbor Tuple with:

               o  N2_2hop_addr := 2-hop address.

               This 2-Hop Tuple (existing or new) is then modified as
               follows:

               o  N2_neighbor_iface_addr_list := Sending Address List;

               o  N2_time := current time + validity time.

           2.  Otherwise, if a 2-hop address has an Address Block TLV
               with:

               o  Type = LINK_STATUS and Value = LOST or Value = HEARD;
                  OR

               o  Type = OTHER_NEIGHB and Value = LOST;

               then remove all 2-Hop Tuples with:

               o  N2_neighbor_iface_addr_list containing one or more
                  network addresses in the Sending Address List; AND

               o  N2_2hop_addr = 2-hop address.

13.  Other Information Base Changes

   The Interface and Neighbor Information Bases MUST be changed when
   certain events occur.  These events may result from HELLO message
   processing or may be otherwise generated (e.g., expiry of timers or
   link quality changes).

   Events that cause changes in the Information Bases are:

   o  A Link Tuple's L_status changes to SYMMETRIC.  In this case, the
      actions specified in Section 13.1 are performed.





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   o  A Link Tuple's L_status changes from SYMMETRIC, or the Link Tuple
      is removed.  In this case, the actions specified in Section 13.2
      are performed.

   o  A Link Tuple's L_HEARD_time expires, or the Link Tuple is removed.
      In this case, the actions specified in Section 13.3 are performed.

   o  Local interface network address changes.  In this case, the
      actions specified in Section 9 are performed.

   o  Link quality changes.  In this case, the actions specified in
      Section 14 are performed.

   If a Link Tuple is removed, or if L_status changes from SYMMETRIC and
   L_HEARD_time expires, then the actions specified in Section 13.2 MUST
   be performed before the actions specified in Section 13.3 are
   performed for that Link Tuple.

   A router MAY report updated information in response to any of these
   changes in HELLO message(s), subject to the constraints in
   Section 11.

   A router that transmits HELLO messages in response to such changes
   SHOULD transmit a HELLO message:

   o  On all MANET interfaces, if the Neighbor Set changes such as to
      indicate the change in symmetry of any 1-hop neighbors (including
      addition or removal of symmetric 1-hop neighbors).

   o  Otherwise, on all those MANET interfaces whose Link Set changes
      such as to indicate a change in L_status of any 1-hop neighbors
      (including the addition or removal of any 1-hop neighbors, other
      than those considered pending).

13.1.  Link Tuple Symmetric

   If, for any Link Tuple that does not have L_status = SYMMETRIC:

   o  L_status changes to SYMMETRIC;

   then:

   1.  For the Neighbor Tuple whose N_neighbor_addr_list contains
       L_neighbor_iface_addr_list, set:

       o  N_symmetric := true.





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   2.  Remove all Lost Neighbor Tuples whose NL_neighbor_addr is
       contained in that N_neighbor_addr_list.

   This includes any newly created Link Tuples whose status is
   immediately updated such that L_status = SYMMETRIC.  (Note that in
   this specification, all Link Tuples are created such that their
   L_status is not SYMMETRIC, but a Link Tuple may be immediately
   updated by subsequent processing of the same HELLO message that
   caused the creation of the Link Tuple such that the Link Tuple's
   L_status changes to SYMMETRIC.)

13.2.  Link Tuple Not Symmetric

   If for any Link Tuple with L_status = SYMMETRIC:

   o  L_status changes to any other value; OR

   o  the Link Tuple is removed;

   then:

   1.  All 2-Hop Tuples for the same MANET interface with:

       o  N2_neighbor_iface_addr_list contains one or more network
          addresses in L_neighbor_iface_addr_list;

       are removed.

   2.  For the Neighbor Tuple whose N_neighbor_addr_list contains
       L_neighbor_iface_addr_list:

       1.  If there are no remaining Link Tuples for any MANET interface
           where:

           o  L_neighbor_iface_addr_list is contained in
              N_neighbor_addr_list; AND

           o  L_status = SYMMETRIC;

           then modify the Neighbor Tuple by:

           1.  N_symmetric := false.

           2.  For each network address (henceforth neighbor address) in
               N_neighbor_addr_list, add a Lost Neighbor Tuple with:

               o  NL_neighbor_addr := neighbor address;




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               o  NL_time := current time + N_HOLD_TIME.

13.3.  Link Tuple Heard Timeout

   If, for any Link Tuple:

   o  L_HEARD_time expires; OR

   o  the Link Tuple is removed;

   then:

   1.  For the Neighbor Tuple whose N_neighbor_addr_list contains
       L_neighbor_iface_addr_list, if no Link Tuples for any MANET
       interface remain where:

       o  L_neighbor_iface_addr_list is contained in
          N_neighbor_addr_list; AND

       o  L_HEARD_time is not expired;

       then remove the Neighbor Tuple.

14.  Link Quality

   Link quality is a mechanism whereby a router MAY take considerations
   other than message exchange into account for determining when a link
   is and is not a candidate for being considered as HEARD or SYMMETRIC.
   As such, it is a "link admission" mechanism.

   Link quality information for a link is generated (e.g., through
   access to signal to noise ratio, packet loss rate, or other
   information from the link layer) and used only locally, i.e., is not
   included in signaling, and routers may interoperate whether they are
   using the same, different, or no, link quality information.  Link
   quality information is specified as a normalized, dimensionless
   figure in the interval zero to one, inclusive, a higher value
   indicating a better link quality.

   For deployments where no link quality is used, the considerations in
   Section 14.1 apply.  For deployments where link quality is used, the
   general principles of link quality usage are described in
   Section 14.2.  Sections 14.3 and 14.4 detail link quality
   functioning.







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14.1.  Deployment without Link Quality

   In order for a router to not employ link quality, the router MUST
   define:

   o  INITIAL_PENDING := false;

   o  INITIAL_QUALITY >= HYST_REJECT (there is no reason not to define
      INITIAL_QUALITY := 1).

14.2.  Basic Principles of Link Quality

   To enable link quality usage, the L_quality value of a Link Tuple is
   used in conjunction with two thresholds, HYST_ACCEPT and HYST_REJECT,
   to set the flags L_pending and L_lost of that Link Tuple.  Based on
   these flags, the link status to advertise for that Link Tuple is
   determined as described in Section 7.1.

   The use of two thresholds implements link hysteresis, whereby a link
   that has HYST_REJECT <= L_quality < HYST_ACCEPT may be either
   accepted or rejected (depending on which threshold it has most
   recently crossed, or, if neither, on the value of parameter
   INITIAL_PENDING).  With appropriate values of these parameters, this
   prevents overly rapid changes of link status.

   The basic principles of link quality usage are as follows:

   o  A router does not advertise a neighbor interface in any state
      until L_quality is acceptable:

      o  If INITIAL_PENDING = true, then the link is advertised when
         link L_quality >= HYST_ACCEPT.

      o  Otherwise, the link is advertised when L_quality >=
         HYST_REJECT.

      A link that is not yet advertised has L_pending = true.

   o  Once L_quality >= HYST_ACCEPT, the router sets L_pending := false,
      indicating that the link can be advertised.

   o  A link for which L_pending = false is advertised until its
      L_quality drops below HYST_REJECT.

   o  If a link has L_pending = false and L_quality < HYST_REJECT, the
      link is LOST and is advertised as such.  This link is not
      reconsidered as a candidate HEARD or SYMMETRIC link until
      L_quality >= HYST_ACCEPT.



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   o  A link that has an acceptable quality may be advertised as HEARD,
      SYMMETRIC or LOST according to the exchange of HELLO messages.

   In order that these principles can all hold, a router MUST NOT
   define:

   o  INITIAL_PENDING = false and INITIAL_QUALITY < HYST_REJECT; OR

   o  INITIAL_PENDING = true and INITIAL_QUALITY >= HYST_ACCEPT.

14.3.  When Link Quality Changes

   If L_quality for a link changes, then the following actions MUST be
   taken:

   1.  If L_quality >= HYST_ACCEPT, then the corresponding Link Tuple is
       modified by:

       1.  L_pending := false;

       2.  L_lost := false;

       3.  If L_status = HEARD or L_status = SYMMETRIC, then:

           o  L_time := max(L_time, L_HEARD_time + L_HOLD_TIME).

   2.  If L_status != PENDING, and L_quality < HYST_REJECT, then the
       corresponding Link Tuple is modified by:

       1.  If L_lost = false, then:

           o  L_lost := true;

           o  L_time := min(L_time, current time + L_HOLD_TIME).

   As a result of this processing, the L_STATUS of a Link Tuple may
   change.  In this case, the processing actions corresponding to this
   change, as specified in Section 13, MUST also be taken.

   If L_quality for a link is updated based on HELLO message reception,
   or on reception of a packet including a HELLO message, then L_quality
   MUST be updated prior to the HELLO message processing described in
   Section 12.  (If the receipt of the HELLO message, or the packet
   containing it, creates the Link Tuple, then the Link Tuple MUST be
   created with the appropriately updated L_quality value, rather than
   with L_quality := INITIAL_QUALITY.)





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14.4.  Updating Link Quality

   A router MAY update link quality based on any information available
   to it.  Particular cases that MAY be used include:

   o  Information from the link layer, such as signal-to-noise ratio or
      packet acknowledgment reception and loss information.

   o  Receipt or loss of control packets.  If control packets include a
      sequential packet sequence number, as defined in [RFC5444], then
      link quality can be updated when a control packet is received,
      whether or not it contains a HELLO message.  The link quality may
      then, for example, be based on whether the last N out of M control
      packets on the link were received, or may use a "leaky integrator"
      tracking packet reception and loss.

   o  Receipt or loss of HELLO messages.  If the maximum interval
      between HELLO messages is known (such as by inclusion in HELLO
      messages of a Message TLV with Type := INTERVAL_TIME, as defined
      in [RFC5497]), then the loss of HELLO messages can be determined
      without the need to receive a later HELLO message.  Note that if
      this case is combined with the previous case, then care must be
      taken to avoid "double counting" a lost HELLO message in a lost
      packet.

15.  Proposed Values for Parameters and Constants

   This section lists the parameters and constants used in the
   specification of the protocol, and proposed values of each that MAY
   be used when a single value of each is used.

15.1.  Message Interval Interface Parameters

   o  HELLO_INTERVAL := 2 seconds

   o  HELLO_MIN_INTERVAL := HELLO_INTERVAL/4

   o  REFRESH_INTERVAL := HELLO_INTERVAL

15.2.  Information Validity Time Interface Parameters

   o  H_HOLD_TIME := 3 x REFRESH_INTERVAL

   o  L_HOLD_TIME := H_HOLD_TIME







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15.3.  Information Validity Time Router Parameters

   o  N_HOLD_TIME := L_HOLD_TIME

   o  I_HOLD_TIME := N_HOLD_TIME

15.4.  Link Quality Interface Parameters

   If link quality is changed, then parameter values will depend on the
   link quality process.  If link quality is not changed, then:

   o  HYST_ACCEPT := 1

   o  HYST_REJECT := 0

   o  INITIAL_QUALITY := 1

   o  INITIAL_PENDING := false

15.5.  Jitter Interface Parameters

   o  HP_MAXJITTER := HELLO_INTERVAL/4

   o  HT_MAXJITTER := HP_MAXJITTER

15.6.  Constants

   o  C := 1/1024 second

16.  Usage with Other Protocols

   Other protocols, such as MANET routing protocols, that use
   neighborhood discovery, may need to interact with this protocol.
   This protocol is designed to permit such interactions, in particular:

   o  Through accessing, and possibly extending, the information in the
      Local Information Base (Section 6), the Interface Information Base
      (Section 7), and the Neighbor Information Base (Section 8).  These
      Information Bases record the interface configuration of the
      router, as well as the local connectivity, up to two hops away.
      All updates to the elements specified in this document are subject
      to the constraints specified in Appendix B.

   o  Through accessing an outgoing HELLO message prior to it being
      transmitted over any MANET interface, and to add information
      (e.g., TLVs) as specified in [RFC5444].  This may, for example, be
      to allow a security protocol, as suggested in Section 17, to add a
      TLV containing a cryptographic signature to the message, or be to



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      allow inserting relay selection information into a HELLO message
      by way of adding a TLV to an outgoing HELLO message prior to it
      being transmitted.

   o  Through accessing an incoming HELLO message, and potentially
      discarding it prior to processing by this protocol.  This may, for
      example, allow a security protocol as suggested in Section 17 to
      perform verification of HELLO message signatures and prevent
      processing of unverifiable HELLO messages by this protocol.

   o  Through accessing an incoming HELLO message after it has been
      completely processed by this protocol.  This may, in particular,
      allow a protocol that has added information, such as relay
      selection information by way of inclusion of appropriate TLVs,
      access to such information after appropriate updates have been
      recorded in the Information Bases in this protocol.

   o  Through requesting that a HELLO message be generated at a specific
      time.  In that case, HELLO message generation MUST still respect
      the constraints in Appendix B.

   Address objects in HELLO messages are processed according to their
   associated Address Block TLVs.  All such address objects are to be
   processed according to this specification are associated with Address
   Block TLVs with Type of LOCAL_IF, OTHER_NEIGHB, or LINK_STATUS (and
   type extension zero).  Address objects not associated with an Address
   Block TLV of any of these Types are therefore not processed by the
   protocol described in this specification.

   A protocol, such as a MANET routing protocol, interacting with this
   protocol may need to add information to HELLO messages.  This may be
   in the form of associating TLVs (of Type other than LOCAL_IF,
   OTHER_NEIGHB, or LINK_STATUS) to address objects already included by
   this specification.

   A protocol, such as a MANET routing protocol, interacting with this
   protocol may also add information to HELLO messages by inserting
   address objects not already included by this specification.  Such
   address objects are in the following called "inserted addresses".
   These inserted addresses may added to Address Blocks already present
   by virtue of the HELLO message generation in this specification, or
   may appear in new Address Blocks.  In both cases, the following MUST
   be observed:

   o  An inserted address MUST NOT be associated with an Address Block
      TLV of Type LOCAL_IF, OTHER_NEIGHB, or LINK_STATUS.  Consequently,
      the processing in this specification will ignore such address
      objects.



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   o  Each inserted address MUST be associated with an Address Block
      TLV, to be defined by the specification of the protocol inserting
      the address object.  In this way, all addresses present in a HELLO
      message are associated with an Address Block TLV defining their
      semantics.

   Informally speaking, Address Block TLVs define the semantics of
   address objects in an Address Block.  If an address object in an
   Address Block does not have any Address Block TLVs associated, that
   address object has no semantics.  Consequently, all protocols using
   the protocol defined in this specification MUST respect the
   following:

   o  An address object in an Address Block, which is not associated
      with any Address Block TLV, MUST be silently ignored; the mere
      presence of an address object without an associated Address Block
      TLV in a HELLO message MUST NOT cause any processing.

   A protocol interacting with this protocol MAY also add an originator
   address to HELLO messages, as specified in [RFC5444].  Such an
   originator address MUST be unique to the originating router, it MAY
   be a local interface address of the router.  It SHOULD be used
   consistently, but SHOULD NOT be constrained in any other way.

   Strict adherence to these points will enable unambiguous coexistence
   of future "extensions" to HELLO messages.

   In some cases, a protocol interacting with the protocol defined in
   this specification, may need to recognize which HELLO messages to
   process and which HELLO messages to discard.  It is the
   responsibility of that protocol to ensure that such messages are
   suitably identifiable, e.g., through inclusion of a Message TLV or
   through recognizing an administrative configuration (such as address
   ranges).  Note that such a protocol interacting with this protocol
   MAY specify such interaction by recognizing an additional reason for
   discarding a message.  As suggested in Section 17 this might, for
   example, be a security protocol discarding a message that does not
   carry a Message TLV containing a cryptographic signature.

17.  Security Considerations

   The objective of this protocol is to allow each router in the network
   to acquire information describing its 1-hop neighborhood and
   symmetric 2-hop neighborhood.  This is acquired through HELLO message
   exchange between neighboring routers.  This information is made
   available through the Interface Information Bases and Neighbor
   Information Base, describing the router's 1-hop neighborhood and
   symmetric 2-hop neighborhood.



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   Under normal circumstances, the information recorded in these
   Information Bases is correct, i.e., corresponds to the actual network
   topology, apart from any changes that have not (yet) been tracked by
   the HELLO message exchanges.

   If a router for some reason, whether malice or malfunction, transmits
   invalid HELLO messages, incorrect information may be recorded in
   other routers' Information Bases.  This protocol specification does,
   however, prevent inconsistent information from being included in the
   Information Bases through the specified processing, which maintains
   the constraints in Appendix B.  The exact consequence of information
   inexactness depends on the use of these Information Bases, and SHOULD
   therefore be reflected in the specification of protocols that use
   information provided by this neighborhood discovery protocol.

   This section, therefore, firstly outlines the ways in which correctly
   formed, but still invalid, HELLO messages may appear, in
   Section 17.1.

   Injection of invalid HELLO messages into a network may be prevented
   in a number of ways.  If, for example, a network is deployed in a
   site to which access is strictly regulated, so that physical access
   and proximity to the network is prevented, then further security
   mechanisms to protect against malicious routers injecting invalid
   HELLO messages may not be required.  Similarly, if the link layer
   over which the network is formed provides appropriate
   confidentiality, authentication, and integrity, then this may, for a
   given deployment, suffice to appropriately protect against disclosure
   of information to an eavesdropper, and against a malicious router
   injecting invalid HELLO messages.  In the latter case, the link layer
   would discard frames that fail the link-layer checks, without
   attempting to deliver such frames to IP.  Finally, certain usage may
   be of a nature where disruption of service is of no consequence, or
   at least not of sufficient consequence to warrant deployment of
   additional security mechanisms.

   A further point to stress, and which follows from the discussions
   above is, that it will not be the case that "one size security fits
   all".  Different deployments may have different requirements.  For
   example, in a deployment of a low-value sensor network,
   authentication using a simple message authentication code and shared
   symmetric keys may suffice, while anything beyond that may require
   too many computational resources to be viable.  Conversely, in, for
   example, a community network, verifying not only that the originator
   of a HELLO message "has the right key" but also the precise identity
   of the originator may be required to be proved, and computational
   resources may be available to make such a requirement feasible.




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   Section 17.2, therefore, does not specify a single "one-size-fits-
   all" mechanism, but rather details how the security suggestions in
   [RFC5444] are considered for applicability within the context of this
   protocol, and with the purpose of aiding deployment-specific security
   mechanisms to be developed.

17.1.  Invalid HELLO Messages

   A correctly formed, but still invalid, HELLO message may take any of
   the following forms.  Note that a present or absent address object in
   an Address Block, does not by itself cause a problem.  It is the
   presence, absence, or incorrectness of associated LOCAL_IF,
   LINK_STATUS, and OTHER_NEIGHB Address Block TLVs that causes
   problems.

   A router may provide false information about its own identity:

      o  The HELLO message may contain address objects with an
         associated LOCAL_IF Address Block TLV that do not correspond to
         addresses of interfaces of the router transmitting the HELLO
         message.

      o  The HELLO message may omit network addresses, or their
         associated LOCAL_IF Address Block TLV, of interfaces of the
         router transmitting the HELLO message (other than the allowed
         omission of the only local interface network address of the
         MANET interface over which the HELLO message is transmitted, if
         that is the case).

      o  The HELLO message may incorrectly specify the LOCAL_IF Address
         Block TLV Value associated with one or more local interface
         network addresses, indicating incorrectly whether they are
         associated with the MANET interface over which the HELLO
         message is transmitted.

   A router may provide false information about the identity of other
      routers:

      o  A present LINK_STATUS Address Block TLV may, incorrectly,
         identify a network address as being of a MANET interface that
         is or was heard on the MANET interface over which the HELLO
         message is transmitted.

      o  A consistently absent LINK_STATUS Address Block TLV may,
         incorrectly, fail to identify a network address as being of a
         MANET interface that is or was heard on the MANET interface
         over which the HELLO message is transmitted.




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      o  A present OTHER_NEIGHB Address Block TLV may, incorrectly,
         identify a network address as being of a router that is or was
         in the sending router's symmetric 1-hop neighborhood.

      o  A consistently absent OTHER_NEIGHB Address Block TLV may,
         incorrectly, fail to identify a network address as being of a
         router that is or was in the sending router's symmetric 1-hop
         neighborhood.

      o  The Value of a LINK_STATUS Address Block TLV may incorrectly
         indicate the status (LOST, SYMMETRIC or HEARD) of the link from
         a 1-hop neighbor.

      o  The Value of an OTHER_NEIGHB Address Block TLV may incorrectly
         indicate the status (LOST or SYMMETRIC) of a symmetric 1-hop
         neighbor.

17.2.  Authentication, Integrity, and Confidentiality Suggestions

   The security suggestions in [RFC5444] regarding inclusion of a
   cryptographic signature in a Message TLV or a Packet TLV can be
   applied to this protocol.  Failure to verify either form of
   cryptographic signature should cause a HELLO message to be rejected
   without being processed.

   The following simplification of the suggestions for end-to-end
   authentication for integrity in [RFC5444] may be applied to HELLO
   messages:

   o  As the Message Header fields <msg-hop-count> and <msg-hop-limit>
      are either omitted or will always have the values 0 and 1,
      respectively, an end to end cryptographic signature can be
      calculated based on the entire HELLO message, including its
      unmodified Message Header.

   The security mechanisms suggested in [RFC5444] with respect to
   confidentiality can be directly applied to this protocol.

18.  IANA Considerations

   This specification defines one Message Type, which has been allocated
   from the "Message Types" registry of [RFC5444], and three Address
   Block TLV Types, which have been allocated from the "Address Block
   TLV Types" registry of [RFC5444].







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18.1.  Expert Review: Evaluation Guidelines

   For the registries where an Expert Review is required, the designated
   expert SHOULD take the same general recommendations into
   consideration as are specified by [RFC5444].

18.2.  Message Types

   This specification defines one Message Type, which has been allocated
   from the 0-223 range of the "Message Types" namespace defined in
   [RFC5444], as specified in Table 3.

                    +------+-------------------------+
                    | Type | Description             |
                    +------+-------------------------+
                    |   0  | HELLO : Local signaling |
                    +------+-------------------------+

                     Table 3: Message Type Assignment

18.3.  Message-Type-Specific TLV Type Registries

   IANA has created a registry for Message-Type-specific Message TLVs
   for HELLO messages, in accordance with Section 6.2.1 of [RFC5444],
   and with initial assignments and allocation policies as specified in
   Table 4.

               +---------+-------------+-------------------+
               |   Type  | Description | Allocation Policy |
               +---------+-------------+-------------------+
               | 128-223 | Unassigned  | Expert Review     |
               +---------+-------------+-------------------+

          Table 4: HELLO Message-Type-specific Message TLV Types

   IANA has created a registry for Message-Type-specific Address Block
   TLVs for HELLO messages, in accordance with Section 6.2.1 of
   [RFC5444], and with initial assignments and allocation policies as
   specified in Table 5.

               +---------+-------------+-------------------+
               |   Type  | Description | Allocation Policy |
               +---------+-------------+-------------------+
               | 128-223 | Unassigned  | Expert Review     |
               +---------+-------------+-------------------+

       Table 5: HELLO Message-Type-specific Address Block TLV Types




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18.4.  Address Block TLV Types

   This specification defines three Address Block TLV Types, which have
   been allocated from the "Address Block TLV Types" namespace defined
   in [RFC5444].  IANA has made allocations in the 0-127 range for these
   types.  Three new type extension registries have been created, with
   assignments as specified in Tables 6, 7, and 8.  Specifications of
   these Address Block TLVs are in Section 10.1.1, with Value Constants
   defined in Section 18.5.

   +----------+------+-----------+------------------------+------------+
   |   Name   | Type |    Type   | Description            | Allocation |
   |          |      | extension |                        | policy     |
   +----------+------+-----------+------------------------+------------+
   | LOCAL_IF |   2  |     0     | Specifies that the     |            |
   |          |      |           | network address is     |            |
   |          |      |           | associated with this   |            |
   |          |      |           | local interface of the |            |
   |          |      |           | sending router         |            |
   |          |      |           | (THIS_IF = 0) or       |            |
   |          |      |           | another local          |            |
   |          |      |           | interface of the       |            |
   |          |      |           | sending router         |            |
   |          |      |           | (OTHER_IF = 1)         |            |
   | LOCAL_IF |   2  |   1-255   | Unassigned             | Expert     |
   |          |      |           |                        | Review     |
   +----------+------+-----------+------------------------+------------+

           Table 6: Address Block TLV Type Assignment: LOCAL_IF

   +-------------+------+-----------+---------------------+------------+
   |     Name    | Type |    Type   | Description         | Allocation |
   |             |      | extension |                     | policy     |
   +-------------+------+-----------+---------------------+------------+
   | LINK_STATUS |   3  |     0     | Specifies the       |            |
   |             |      |           | status of the link  |            |
   |             |      |           | from the indicated  |            |
   |             |      |           | network address     |            |
   |             |      |           | (LOST = 0,          |            |
   |             |      |           | SYMMETRIC = 1, or   |            |
   |             |      |           | HEARD = 2)          |            |
   | LINK_STATUS |   3  |   1-255   | Unassigned          | Expert     |
   |             |      |           |                     | Review     |
   +-------------+------+-----------+---------------------+------------+

          Table 7: Address Block TLV Type Assignment: LINK_STATUS





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   +--------------+------+-----------+--------------------+------------+
   |     Name     | Type |    Type   | Description        | Allocation |
   |              |      | extension |                    | policy     |
   +--------------+------+-----------+--------------------+------------+
   | OTHER_NEIGHB |   4  |     0     | Specifies the      |            |
   |              |      |           | status of the      |            |
   |              |      |           | relationship with  |            |
   |              |      |           | the router that    |            |
   |              |      |           | uses the indicated |            |
   |              |      |           | network address on |            |
   |              |      |           | one or more        |            |
   |              |      |           | interfaces (LOST = |            |
   |              |      |           | 0, or SYMMETRIC =  |            |
   |              |      |           | 1)                 |            |
   | OTHER_NEIGHB |   4  |   1-255   | Unassigned         | Expert     |
   |              |      |           |                    | Review     |
   +--------------+------+-----------+--------------------+------------+

         Table 8: Address Block TLV Type Assignment: OTHER_NEIGHB

18.5.  LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB Values

   Note: This information is recorded here for clarity and for use
   elsewhere in this specification.  The information required by IANA is
   included in the descriptions of the Address Block TLVs allocated in
   Section 18.4.

   The Values that the LOCAL_IF Address Block TLV can use are the
   following:

   o  THIS_IF := 0

   o  OTHER_IF := 1

   The Values that the LINK_STATUS Address Block TLV can use are the
   following:

   o  LOST := 0

   o  SYMMETRIC := 1

   o  HEARD := 2

   The Values that the OTHER_NEIGHB Address Block TLV can use are the
   following:

   o  LOST := 0




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   o  SYMMETRIC := 1

19.  Contributors

   This specification is the result of the joint efforts of the
   following contributors from the OLSRv2 Design Team, listed
   alphabetically:

   o  Brian Adamson, NRL, USA, <adamson@itd.nrl.navy.mil>

   o  Cedric Adjih, INRIA, France, <Cedric.Adjih@inria.fr>

   o  Thomas Heide Clausen, LIX, France, <T.Clausen@computer.org>

   o  Justin Dean, NRL, USA, <jdean@itd.nrl.navy.mil>

   o  Christopher Dearlove, BAE Systems ATC, UK,
      <chris.dearlove@baesystems.com>

   o  Philippe Jacquet, INRIA, France, <Philippe.Jacquet@inria.fr>

20.  Acknowledgments

   The authors would like to acknowledge the team behind OLSRv1,
   specified in RFC3626 for their contributions.

   The authors would like to gratefully acknowledge the following people
   for intense technical discussions, early reviews and comments on the
   specification and its components (listed alphabetically): Alan Cullen
   (BAE Systems), Ulrich Herberg (LIX), Satoh Hiroki (Hitachi) Joe
   Macker (NRL), Charles E. Perkins (WiChorus), Laurent Viennot (INRIA),
   and the entire IETF MANET working group.



















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21.  References

21.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5148]  Clausen, T., Dearlove, C., and B. Adamson, "Jitter
              Considerations in Mobile Ad Hoc Networks (MANETs)",
              RFC 5148, February 2008.

   [RFC5444]  Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
              "Generalized Mobile Ad Hoc Network (MANET) Packet/Message
              Format", RFC 5444, February 2009.

   [RFC5497]  Clausen, T. and C. Dearlove, "Representing Multi-Value
              Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497,
              March 2009.

   [RFC5498]  Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network
              (MANET) Protocols", RFC 5498, March 2009.

21.2.  Informative References

   [RFC2501]  Corson, M. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501, January 1999.

   [RFC3626]  Clausen, T. and P. Jacquet, "Optimized Link State Routing
              Protocol (OLSR)", RFC 3626, October 2003.

   [RFC5449]  Baccelli, E., Jacquet, P., Nguyen, D., and T. Clausen,
              "OSPF Multipoint Relay (MPR) Extension for Ad Hoc
              Networks", RFC 5449, February 2009.

















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Appendix A.  Address Block TLV Combinations

   The algorithm for generating HELLO messages in Section 11 specifies
   which 1-hop neighbor network addresses may be included in the Address
   Blocks, and with which associated Address Block TLVs.  These Address
   Block TLVs may have Type = LINK_STATUS or Type = OTHER_NEIGHB, or
   both.  Address Block TLVs with Type = LINK_STATUS may have three
   possible Values (Value = HEARD, Value = SYMMETRIC, or Value = LOST),
   and Address Block TLVs of TYPE = OTHER_NEIGHB may have two possible
   Values (Value = SYMMETRIC or Value = LOST).  When both Address Block
   TLVs are associated with the same network address only certain
   combinations of these Address Block TLV Values are necessary, and are
   the only combinations generated by the algorithm in Section 11.
   These combinations are indicated in Table 9.

   Cells labeled with "Yes" indicate the possible combinations that are
   generated by the algorithm in Section 11.  Cells labeled with "No"
   indicate combinations not generated by the algorithm in Section 11
   but that are correctly parsed and interpreted by the algorithm in
   Section 12.  The cell labeled with "No*" is actually inconsistent, it
   is handled by ignoring the Address Block TLV with Type =
   OTHER_NEIGHB, but SHOULD NOT be used.

   +----------------+----------------+----------------+----------------+
   |                |     Type =     |     Type =     |     Type =     |
   |                |  OTHER_NEIGHB  |  OTHER_NEIGHB, |  OTHER_NEIGHB, |
   |                |    (absent)    |     Value =    |  Value = LOST  |
   |                |                |    SYMMETRIC   |                |
   +----------------+----------------+----------------+----------------+
   | Type =         |       No       |       Yes      |       Yes      |
   | LINK_STATUS    |                |                |                |
   | (absent)       |                |                |                |
   | Type =         |       Yes      |       Yes      |       Yes      |
   | LINK_STATUS,   |                |                |                |
   | Value = HEARD  |                |                |                |
   | Type =         |       Yes      |       No       |       No*      |
   | LINK_STATUS,   |                |                |                |
   | Value =        |                |                |                |
   | SYMMETRIC      |                |                |                |
   | Type =         |       Yes      |       Yes      |       No       |
   | LINK_STATUS,   |                |                |                |
   | Value = LOST   |                |                |                |
   +----------------+----------------+----------------+----------------+

          Table 9: LINK_STATUS and OTHER_NEIGHB TLV Combinations






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Appendix B.  Constraints

   Any process that updates the Local Information Base or the Neighbor
   Information Base MUST ensure that all constraints specified in this
   appendix are maintained.

   In each Local Interface Tuple:

   o  I_local_iface_addr_list MUST NOT be empty.

   o  I_local_iface_addr_list MUST NOT contain any duplicated network
      addresses.

   o  If I_manet = true, then I_local_iface_addr_list MUST NOT contain
      any network address that overlaps any network address in the
      I_local_iface_addr_list of any other Local Interface Tuple with
      I_manet = true, unless it is known that the corresponding MANET
      interfaces will always communicate with separate sets of MANET
      interfaces on other routers.

   In each Removed Interface Address Tuple:

   o  IR_local_iface_addr MUST NOT contain any network address that is
      in the I_local_iface_addr_list of any Local Interface Tuple.

   o  IR_local_iface_addr MUST NOT equal the IR_local_iface_addr of any
      other Removed Interface Address Tuple.

   In each Link Tuple:

   o  L_neighbor_iface_addr_list MUST NOT be empty.

   o  L_neighbor_iface_addr_list MUST NOT contain any network address
      that overlaps any network address in the I_local_iface_addr_list
      of any Local Interface Tuple or the IR_local_iface_addr of any
      Removed Interface Address Tuple.

   o  L_neighbor_iface_addr_list MUST NOT contain any duplicated network
      addresses.

   o  L_neighbor_iface_addr_list MUST NOT contain any network address
      which is in the L_neighbor_iface_addr_list of any other Link Tuple
      in the same Link Set.

   o  If L_HEARD_time has not expired, then there MUST be a Neighbor
      Tuple whose N_neighbor_addr_list contains
      L_neighbor_iface_addr_list.




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   o  L_HEARD_time MUST NOT be greater than L_time.

   o  L_SYM_time MUST NOT be greater than L_HEARD_time (unless both are
      expired).

   o  L_quality MUST NOT be less than 0 or greater than 1.

   o  If L_quality >= HYST_ACCEPT, then L_pending MUST be false.

   o  If L_quality < HYST_REJECT, then L_status MUST be PENDING or LOST.

   o  L_pending MUST NOT be set to true if it is currently false.

   In each Neighbor Tuple:

   o  N_neighbor_addr_list MUST NOT contain any network address that
      overlaps any network address in the I_local_iface_addr_list of any
      Local Interface Tuple or the IR_local_iface_addr of any Removed
      Interface Address Tuple.

   o  N_neighbor_addr_list MUST NOT contain any duplicated network
      addresses.

   o  N_neighbor_addr_list MUST NOT contain any network address that is
      in the N_neighbor_addr_list of any other Neighbor Tuple.

   o  If N_symmetric is = true, then there MUST be one or more Link
      Tuples with:

      o  L_neighbor_iface_addr_list contained in N_neighbor_addr_list;
         AND

      o  L_status = SYMMETRIC.

   o  If N_symmetric is = false, then there MUST be one or more Link
      Tuples with:

      o  L_neighbor_iface_addr_list contained in N_neighbor_addr_list.

      All such Link Tuples MUST NOT have L_status = SYMMETRIC.  At least
      one such Link Tuple MUST have L_HEARD_time not expired.

   In each Lost Neighbor Tuple:

   o  NL_neighbor_addr MUST NOT overlap any network address in the
      I_local_iface_addr_list of any Local Interface Tuple or the
      IR_local_iface_addr of any Removed Interface Address Tuple.




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   o  NL_neighbor_addr MUST NOT equal the NL_neighbor_addr of any other
      Lost Neighbor Tuple.

   o  NL_neighbor_addr MUST NOT be in the N_neighbor_addr_list of any
      Neighbor Tuple with N_symmetric = true.

   In each 2-Hop Tuple:

   o  There MUST be a Link Tuple associated with the same MANET
      interface with:

      o  L_neighbor_iface_addr_list = N2_neighbor_iface_addr_list; AND

      o  L_status = SYMMETRIC.

   o  N2_2hop_addr MUST NOT overlap any network address in the
      I_local_iface_addr_list of any Local Interface Tuple or the
      IR_local_iface_addr of any Removed Interface Address Tuple.

   o  N2_2hop_addr MUST NOT be the N2_2hop_addr of any other 2-Hop Tuple
      in the same 2-Hop Set and with the same
      N2_neighbor_iface_addr_list.

   o  N2_2hop_addr MUST NOT be in the N2_neighbor_iface_addr_list of the
      same 2-Hop Tuple.

Appendix C.  HELLO Message Example

   HELLO messages are instances of [RFC5444] messages, and this protocol
   supports any combination of message header options and address
   encodings, enabled by [RFC5444] that convey the required information.
   As a consequence, there is no single way to represent how all HELLO
   messages look.  This appendix illustrates two HELLO message with
   similar content, the exact values included are explained in the
   following text.

   The HELLO message's four bit Message Flags (MF) field has value 7
   indicating that the message header contains hop limit, hop count, and
   message sequence number fields.  Its four bit Message Address Length
   (MAL) field has value 3, indicating addresses in the message have a
   length of four octets, here being IPv4 addresses.  The message is as
   transmitted, with a hop limit of 1 and a hop count of 0.  The overall
   message length is 45 octets.

   The message contains a Message TLV Block with content length 8 octets
   containing two Message TLVs, of types VALIDITY_TIME and
   INTERVAL_TIME.  Each uses a Message TLV with Flags octet (MTLVF)
   value 16, indicating that each has a Value, and each has a Value



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   Length of 1 octet.  The Values included are time codes (as defined in
   [RFC5497]) representing the parameters H_HOLD_TIME and
   HELLO_INTERVAL, respectively.

   The message has a single Address Block containing 5 addresses.  The
   Address Block Flags octet (ABF) value 128 indicates an address Head
   but no address Tail, and no address prefixes.  The Head Length of 3
   octets indicates address Mid sections of one octet each (Mid 0 to Mid
   4).

   The following Address Block TLV Block (content length 14 octets)
   includes two Address Block TLVs.  The first is a LOCAL_IF Address
   Block TLV with Flags octet (ATLVF) value 80, which indicates that a
   single address, with index 0 (i.e., the address Head:Mid 0) is the
   single local interface address of this router (the one octet Value
   THIS_IF indicates that this address is of this interface).  The
   second is a LINK_STATUS Address Block TLV with Flags octet (ATLVF)
   value 52, which specifies the link status values of all reported
   neighbors in a single multivalue Address Block TLV that covers the
   addresses with indexes 1 to 4, inclusive.  The Address Block TLV
   Value Length of 4 octets indicates one octet per Value per address.
   The last four addresses thus are of neighbors, each an with
   associated link status: the first and second HEARD, the third
   SYMMETRIC, and the fourth LOST.



























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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     HELLO     | MF=7  | MAL=3 |      Message Length = 45      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Hop Limit = 1 | Hop Count = 0 |    Message Sequence Number    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Message TLV Block Length = 8  | VALIDITY_TIME |  MTLVF = 16   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Value Len = 1 | Value (Time)  | INTERVAL_TIME |  MTLVF = 16   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Value Len = 1 | Value (Time)  | Num Addrs = 5 |   ABF = 128   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Head Len = 3  |                     Head                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Mid 0     |     Mid 1     |     Mid 2     |     Mid 3     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Mid 4     | Address TLV Block Length = 14 |   LOCAL_IF    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  ATLVF = 80   |   Index = 0   | Value Len = 1 |    THIS_IF    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  LINK_STATUS  |   ATLV = 52   | Strt Indx = 1 | Stop Indx = 4 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Value Len = 4 |     HEARD     |     HEARD     |   SYMMETRIC   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     LOST      |
     +-+-+-+-+-+-+-+-+

   Note that this example is for illustrative purposes.  The essential
   information can be conveyed, more efficiently (assuming that the
   local interface address will be supplied by IP, and that the
   INTERVAL_TIME TLV is not needed) by the 29 octets:



















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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     HELLO     |0 0 0 0 0 0 1 1|0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0| VALIDITY_TIME |0 0 0 1 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 1 1 0 0 1 0 0|0 0 0 0 0 1 0 0|1 0 0 0 0 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 1 1|                     Head                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Mid 1     |     Mid 2     |     Mid 3     |     Mid 4     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1|  LINK_STATUS  |0 0 0 1 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 1 0 0|     HEARD     |     HEARD     |   SYMMETRIC   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     LOST      |
     +-+-+-+-+-+-+-+-+

   Note that the above example assumes that H_HOLD_TIME and C have their
   default values of 6 seconds and 1/1024 second, and thus result in a
   time code of 100 (hexadecimal 64).

Appendix D.  Flow and Congestion Control

   This protocol specifies one Message Type, the HELLO message.  The
   maximum size of a HELLO message is proportional to the size of the
   originating router's 1-hop neighborhood.  HELLO messages MUST NOT be
   forwarded.

   A router MUST report its 1-hop neighborhood in HELLO messages on each
   of its MANET interfaces at least each REFRESH_INTERVAL.  This puts a
   lower bound on the control traffic generated by each router in the
   network employing this protocol.

   A router MUST ensure that two successive HELLO messages sent on the
   same MANET interface are separated by at least HELLO_MIN_INTERVAL.
   (If using jitter, then this may be reduced to a mean minimum value of
   HELLO_MIN_INTERVAL - HP_MAXJITTER/2.)  Thus, this puts an upper bound
   on the control traffic generated by each router in the network
   employing this protocol.









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Appendix E.  Interval and Timer Illustrations

   This informative appendix illustrates the relationship between
   message timers and intervals.  (The adjustments to this timing when
   using timing jitter, as defined in [RFC5148], are not shown.)

E.1.  HELLO Message Generation Timing

   Figure 1 illustrates a basic HELLO message schedule for a router, on
   a MANET interface, employing strictly periodic transmission of HELLO
   messages.  The router transmits a HELLO message each HELLO_INTERVAL.
   Each HELLO message contains all 1-hop neighbor network addresses of
   the router that are to be reported in any such HELLO message.  (The
   parameter REFRESH_INTERVAL, not shown, is in this example equal to
   the parameter HELLO_INTERVAL.)

   The router includes a VALIDITY_TIME TLV in each HELLO message,
   encoding the parameter H_HOLD_TIME, the duration for which
   information received in the HELLO message should be considered valid
   by receiving routers.  Receiving routers will, when recording the
   information received in the HELLO message, each use this for setting
   the L_HEARD_time, L_SYM_time and L_time elements of their
   corresponding Link Tuple, and the N2_time in the corresponding 2-Hop
   Tuple for each network address.  Only L_time is illustrated in
   Figure 1.

     H_HOLD_TIME:         |-----------------------------|   ...

     HELLO_INTERVAL:      |---------|---------|---------|   ...

     Time:             ---*---------*---------*---------*------>

                          ^         ^         ^         ^
                          |         |         |         |
         HELLO (a, b, c, d)         |         |         |
                                    |         |         |
                   HELLO (a, b, c, d)         |         |   ...
                                              |         |
                             HELLO (a, b, c, d)         |
                                                        |
                                       HELLO (a, b, c, d)

     L_time:              |-----------------------------|
                                    |--------------------   ...
                                              |----------   ...
                                                        |   ...

           Figure 1: HELLO Message Generation: Regular Schedule



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   Figure 2 illustrates a message schedule similar to Figure 1, where
   the router announces its own presence more frequently by sending
   additional HELLO messages.  HELLO messages are still sent regularly,
   at a reduced interval defined by a new value of HELLO_INTERVAL.
   However, REFRESH_INTERVAL has not been reduced.  Each 1-hop neighbor
   network address included in these HELLO messages need be advertised
   only once within each REFRESH_INTERVAL.  Consequently, the additional
   HELLO messages due to the reduced value of HELLO_INTERVAL may
   therefore be empty.  (This is not the only allowed distribution of
   1-hop neighbor network addresses, they could, for example, be sent
   alternately a, b and c, d.)

     H_HOLD_TIME:         |-----------------------------|   ...

     REFRESH_INTERVAL:    |---------|---------|---------|   ...

     HELLO_INTERVAL:      |----|----|----|----|----|----|   ...

     Time:             ---*---------*---------*---------*------>

                          ^    ^    ^    ^    ^    ^    ^
                          |    |    |    |    |    |    |
         HELLO (a, b, c, d)    |    |    |    |    |    |
                               |    |    |    |    |    |
                        HELLO ()    |    |    |    |    |
                                    |    |    |    |    |
                   HELLO (a, b, c, d)    |    |    |    |
                                         |    |    |    |   ...
                                  HELLO ()    |    |    |
                                              |    |    |
                             HELLO (a, b, c, d)    |    |
                                                   |    |
                                            HELLO ()    |
                                                        |
                                       HELLO (a, b, c, d)

     L_time:              |-----------------------------|
                               |-------------------------   ...
                                    |--------------------   ...
                                         |---------------   ...
                                              |----------   ...
                                                   |-----   ...
                                                        |   ...

    Figure 2: HELLO Message Generation: Regular Schedule with Different
                    HELLO_INTERVAL and REFRESH_INTERVAL





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   HELLO messages may also be sent in response to events.  The minimal
   interval between two successive HELLO message transmissions by a
   router is HELLO_MIN_INTERVAL, setting an upper bound of the HELLO
   message emission rate.  Hence, for each HELLO message transmission, a
   router must wait at least HELLO_MIN_INTERVAL before the next HELLO
   message transmission.  Similarly, the maximum interval between two
   successive HELLO message transmissions is HELLO_INTERVAL, setting a
   lower bound on the message transmission rate.  Hence, for each HELLO
   message transmission, the router must ensure that the next HELLO
   message transmission must not wait more than HELLO_INTERVAL.

   Figure 3 illustrates a message schedule similar to Figure 1, but with
   HELLO messages responding to events at maximum rate, i.e., with HELLO
   messages being sent each HELLO_MIN_INTERVAL.  Note that when a HELLO
   message is sent, it is assumed that the following messages may all be
   scheduled at an interval of HELLO_INTERVAL, and hence each HELLO
   message contains all 1-hop neighbor network addresses.  In each HELLO
   message in this example, a new 1-hop neighbor network address is
   added, reflecting the changes occurring since the last HELLO message
   was sent.  HELLO messages are sent at the maximum allowed rate in
   order to signal these changes as rapidly as possible.






























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     H_HOLD_TIME:         |-----------------------------|   ...

     HELLO_INTERVAL:      |---------|---------|---------|   ...

     HELLO_MIN_INTERVAL:  |----|----|----|----|----|----|   ...

     Time:             ---*---------*---------*---------*------>

                          ^    ^    ^    ^    ^    ^    ^
                          |    |    |    |    |    |    |
                   HELLO ()    |    |    |    |    |    |
                               |    |    |    |    |    |
                       HELLO (a)    |    |    |    |    |
                                    |    |    |    |    |
                         HELLO (a, b)    |    |    |    |
                                         |    |    |    |   ...
                           HELLO (a, b, c)    |    |    |
                                              |    |    |
                             HELLO (a, b, c, d)    |    |
                                                   |    |
                               HELLO (a, b, c, d, e)    |
                                                        |
                                 HELLO (a, b, c, d, e, f)

     L_time:              |-----------------------------|
                               |-------------------------   ...
                                    |--------------------   ...
                                         |---------------   ...
                                              |----------   ...
                                                   |-----   ...
                                                        |   ...

   Figure 3: HELLO Message Generation: Regular Schedule with Responsive
                                 Messages

   Figure 4 shows the same example as Figure 3, but with an increased
   REFRESH_INTERVAL, and showing partial HELLO messages that include
   only the necessary network addresses.













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     H_HOLD_TIME:         |-----------------------------|   ...

     REFRESH_INTERVAL:    |-------------------|----------   ...
                               |-------------------|-----   ...
                                    |-------------------|   ...
                                         |---------------   ...
                                              |----------   ...
                                                   |-----   ...
                                                        |   ...

     HELLO_INTERVAL:      |---------|---------|---------|   ...

     HELLO_MIN_INTERVAL:  |----|----|----|----|----|----|   ...

     Time:             ---*---------*---------*---------*------>

                          ^    ^    ^    ^    ^    ^    ^
                          |    |    |    |    |    |    |
                   HELLO ()    |    |    |    |    |    |
                               |    |    |    |    |    |
                       HELLO (a)    |    |    |    |    |
                                    |    |    |    |    |
                            HELLO (b)    |    |    |    |
                                         |    |    |    |   ...
                                 HELLO (c)    |    |    |
                                              |    |    |
                                   HELLO (a, d)    |    |
                                                   |    |
                                        HELLO (b, e)    |
                                                        |
                                             HELLO (c, f)

     L_time:              |-----------------------------|
                               |-------------------------   ...
                                    |--------------------   ...
                                         |---------------   ...
                                              |----------   ...
                                                   |-----   ...
                                                        |   ...

   Figure 4: HELLO Message Generation: Regular Schedule with Responsive
        Messages and Different HELLO_INTERVAL and REFRESH_INTERVAL









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   Figure 5 summarizes the overall relationship between the intervals
   governing HELLO message transmissions by a router.

     H_HOLD_TIME:         |------------------------------------|

     REFRESH_INTERVAL:    |----------------|

     HELLO_INTERVAL:      |----------|

     HELLO_MIN_INTERVAL:  |---|

     Time:             ----------------------------------------------->

                          ^   ^      ^     ^                   ^
                          |   |      |     |                   |
                          |   |      |     |           Time up to which
              HELLO message   |      |     |           received HELLO
              transmission    |      |     |           message content
                              |      |     |           is valid.
                              |      |     |
                              |      |     Time before which all
                              |      |     neighbor information must
                              |      |     be transmitted in HELLO
                              |      |     messages (one or more)
                              |      |
                              |      Latest time for next HELLO message
                              |      transmission
                              |
                              Earliest time for next HELLO message
                              transmission

               Figure 5: HELLO Message Generation Intervals



















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E.2.  HELLO Message Processing Timing

   Figure 6 illustrates the Link Set timers when receiving a HELLO
   message not including the network address of the receiving MANET
   interface.

     VALIDITY_TIME:    |--------------------------|

     L_time:           |--------------------------|

     L_HEARD_time:     |--------------------------|

     L_SYM_time:     *-| (i.e.,  expired)

     Time:          ---*-------------------------------->
                       ^
                       |
                HELLO () received

      Figure 6: HELLO Message Processing: Network Address Not Present

   Figure 7 illustrates the Link Set timers when, following the received
   HELLO message illustrated in Figure 6, a router receives a HELLO
   message including the network address (a) of the receiving interface
   with link status = HEARD (or SYM).

     VALIDITY_TIME:    |--------------------------|
                             |--------------------------|

     L_time:           |--------------------------|
                             |--------------------------|

     L_HEARD_time:     |--------------------------|
                             |--------------------------|

     L_SYM_time:     *-| (i.e.,  expired)
     L_SYM_time:             |--------------------------|

     Time:            -*-----*--------------------------------->
                       ^     ^
                       |     |
      HELLO () received      |
                             |
      HELLO (a:HEARD) received

        Figure 7: HELLO Message Processing: Network Address Present





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   Figure 8 illustrates the Link Set timers when, following the received
   HELLO messages illustrated in Figure 7, a router receives a HELLO
   message including the network address (a) of the receiving interface
   with link status = LOST.

     VALIDITY_TIME:    |--------------------------|
                             |--------------------------|
                                   |--------------------------|

     L_time:           |--------------------------|
                             |--------------------------|
                                   |--------------------------|

     L_HEARD_time:     |--------------------------|
                             |--------------------------|
                                   |--------------------------|

     L_SYM_time:     *-| (i.e.,  expired)
                             |--------------------------|
                                 *-| (i.e.,  expired)

     Time:            -*-----*-----*--------------------------------->
                       ^     ^     ^
                       |     |     |
       HELLO () received     |     |
                             |     |
      HELLO (a:HEARD) received     |
                                   |
             HELLO (a:LOST) received

         Figure 8: HELLO Message Processing: Network Address Lost

E.3.  Other HELLO Message Timing

   There are three other timing parameters that are used by a router to
   control HELLO message generation and processing.

   Figure 9 illustrates the time, with duration L_HOLD_TIME, during
   which the appropriate network addresses of a formerly, but no longer,
   symmetric 1-hop neighbor, as connected by this MANET interface, are
   advertised as LOST using a LINK_STATUS TLV in HELLO messages on this
   MANET interface, thus allowing that 1-hop neighbor to update its Link
   Set accordingly.








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     L_HOLD_TIME:   |----------------------------|

     Time:       ---*---------------------------------->
                    ^                            ^
                    |                            |
         Formerly symmetric 1-hop neighbor       |
         ceases to be symmetric on this          |
         MANET interface                         |
                                                 |
                      Time up to which network addresses of
                      this neighbor connected using this MANET
                      interface are advertised in HELLO
                      messages on this MANET interface
                      using a LINK_STATUS TLV, Value = LOST

       Figure 9: HELLO Message Generation: Advertisement of Formerly
         Symmetric 1-Hop Neighbor on This MANET Interface as Lost

   Figure 10 illustrates the time, with duration N_HOLD_TIME, during
   which all network addresses of a formerly, but no longer, symmetric
   1-hop neighbor, are advertised as LOST in HELLO messages on all MANET
   interfaces using an OTHER_NEIGHB TLV (if not also reported using a
   LINK_STATUS TLV) thus allowing all other symmetric 1-hop neighbors to
   update their 2-Hop Sets accordingly.

     L_HOLD_TIME:   |----------------------------|

     Time:       ---*---------------------------------->
                    ^                            ^
                    |                            |
         Formerly symmetric 1-hop neighbor       |
         ceases to be symmetric                  |
                                                 |
                      Time up to which network addresses of
                      this neighbor are advertised in HELLO
                      messages on all MANET interfaces
                      using an OTHER_NEIGHB TLV,
                      Value = LOST

      Figure 10: HELLO Message Generation: Advertisement of Formerly
          Symmetric 1-Hop Neighbor on Any MANET Interface as Lost

   Figure 11 illustrates the time, with duration I_HOLD_TIME, during
   which a formerly, but no longer, used local interface network address
   is excluded from being considered as a 2-hop neighbor network address
   (in order that a router is not recorded as its own 2-hop neighbor
   during that period).




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     I_HOLD_TIME:      |----------------------------|

     Time:          ---*----------------------------------->
                       ^                            ^
                       |                            |
       Formerly used local interface                |
       network address ceases to be                 |
       assigned to a local interface                |
                                                    |
                               Time up to which this network
                               address is excluded from being
                               included in this router's 2-Hop Set

            Figure 11: Local Interface Removed Network Address

Appendix F.  Topology Pictures

   This appendix illustrates various examples of physical topologies, as
   well as how these are logically recorded by NHDP from the point of
   view of the router A.  This representation is a composite of
   information that would be contained within A's various Information
   Bases after NHDP has been running for sufficiently long time for the
   state to converge.

   Note that the examples given in this appendix are NOT exhaustive, but
   are selected to be illustrative of NHDP neighborhood representations
   of physical MANET topologies.

   The example topologies presented contain 3 physical routers A, B, and
   C.   Each of these routers has one or two distinct interfaces,
   denoted "top" and "bottom".  Each interface has one or two addresses,
   and symmetric connectivity between a pair of interfaces is
   illustrated by these being connected by a line.

   In all examples, the topology is described as it is recorded by NHDP
   in router A.

F.1.  Example 1: Standard Single Interface Topology

   In Figure 12, each router has a single interface, each with a single
   IP address.  This is the simplest possible network, and the resulting
   representation is given to the right in Figure 12.









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         __________ __________
        |          |          |
       {1}        {2}        {3}
        |          |          |              {1}--------{2}--------{3}
     +--'--+    +--'--+    +--'--+
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+

         Figure 12: Standard Single Interface Topology (Left), and
                 Corresponding NHDP Representation (Right)

   The Local Information Set in A contains a single Local Interface
   Tuple that has an I_local_iface_addr_list of {1}.  This value is
   denoted with a {1} on the leftmost part of the resulting
   representation.

   The Interface Information Base has only one Link Set, which
   represents the "top" interface of A, or {1}.  This Link Set's only
   Link Tuple has an L_neighbor_iface_addr_list containing {2}; this
   corresponds to the dashed line from {1} to {2} to the right in
   Figure 12.  The 2-Hop Set contains a single 2-Hop Tuple, with
   N2_neighbor_iface_addr_list being {2} and N2_2hop_addr being {3};
   this corresponds to the dashed line from {2} to {3} to the right in
   Figure 12.

   The descriptions of the following examples in this appendix will be
   derived similarly, and use the same notational conventions.

F.2.  Example 2: Dual Addressed Interface on 1-Hop Neighbor

   In Figure 13, the network is identical to that in Example 1, except
   that the middle router, B, has two IP addresses on its single
   interface.

         __________ __________
        |          |          |
       {1}       {2,4}       {3}
        |          |          |              {1}-------{2,4}-------{3}
     +--'--+    +--'--+    +--'--+
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+

      Figure 13: Single Interfaces, with 1-Hop Neighbor B Having Two
      Addresses (Left), and Corresponding NHDP Representation (Right)







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   The content of the Interface Information Base is in this case
   identical to Example 1, except that L_neighbor_iface_addr_list is
   {2,4} and N2_neighbor_iface_addr_list is {2,4}.

F.3.  Example 3: Dual Addressed Interface on 2-Hop Neighbor

   In Figure 14, the network is identical to that in Example 1, except
   that the rightmost router, C, has two IP addresses on its interface.

         __________ __________
        |          |          |
       {1}        {2}       {3,4}                             +----{3}
        |          |          |              {1}--------{2}---+
     +--'--+    +--'--+    +--'--+                            +----{4}
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+

      Figure 14: Single Interfaces, with 2-Hop Neighbor C Having Two
      Addresses (Left), and Corresponding NHDP Representation (Right)

   The content of the Interface Information Base is in this case
   identical to than in Example 1, except that the 2-Hop Set contains an
   extra 2-Hop Tuple with N2_neighbor_iface_addr_list being {2} and
   N2_2hop_addr being {4}.  These two 2-Hop Tuples are illustrated by
   the two lines from {2} to {3} and (2) to {4}, respectively.

F.4.  Example 4: Dual Addressed Interfaces

   In Figure 15, the network is identical to that in Example 1, except
   that all routers have two IP addresses on their interface.  The Local
   Information Base in router A is the same as in Example 1, except that
   I_local_iface_addr_list is {1,5}.

         __________ __________
        |          |          |
      {1,5}      {2,6}      {3,4}                             +----{3}
        |          |          |             {1,5}------{2,6}--+
     +--'--+    +--'--+    +--'--+                            +----{4}
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+

      Figure 15: Single interfaces, all routers having two addresses
           (left), and corresponding NHDP representation (right)

   The content of the Interface Information Base is in this case a
   combination of the Interface Information Bases from Examples 1, 2,
   and 3.




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F.5.  Example 5: Dual Interface on 2-Hop Neighbor

   In Figure 16, all routers have a single IP address on each interface,
   and with the 2-hop neighbor having two interfaces.

         __________ __________
        |          |          |
       {1}        {2}        {3}                              +----{3}
        |          |          |              {1}--------{2}---+
     +--'--+    +--'--+    +-----+                            +----{4}
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+
                              |
                             {4}

       Figure 16: Single Addresses, with 2-Hop Neighbor C Having Two
     Interfaces (Left), and Corresponding NHDP Representation (Right)

   The Interface Information Base is identical to that in Example 3;
   NHDP does not distinguish topologically between this example and
   Example 3.

F.6.  Example 6: Dual interface on 1-Hop Neighbor

   In Figure 17, all routers have a single IP address on each interface,
   and with the 1-hop neighbor having two interfaces.

         __________
        |          |
       {1}        {2}                                  +-----+
        |          |                         {1}-------| {2} |------{4}
     +--'--+    +--'--+    +-----+                     | {5} |
     |  A  |    |  B  |    |  C  |                     +-----+
     +-----+    +-----+    +-----+
                   |          |
                  {5}        {4}
                   |__________|

       Figure 17: Single Addresses, with 1-Hop Neighbor B Having Two
     Interfaces (Left), and Corresponding NHDP Representation (Right)

   The Local Information Base is identical to that in Example 1.

   The Interface Information Base has only one Link Set containing one
   Link Tuple with L_neighbor_iface_addr_list being {2}.  The 2-Hop Set
   contains a single 2-Hop Tuple, with N2_neighbor_iface_addr_list being
   {2} and N2_2hop_addr being {4}.




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   The Neighbor Information Base contains a Neighbor Set containing a
   single Neighbor Tuple, which represents router B, with
   N_neighbor_addr_list being {2,5}.  This entry is represented on the
   right of Figure 17 by boxing {2} with {5}.

   Note that router A does not have information indicating which of
   router B's interfaces is connected to router C.  However, router A
   knows that the address {4} (and thus router C) is reachable by using
   {2} as next hop.

F.7.  Example 7: Dual Interface on 1-Hop and 2-Hop Neighbors

   In Figure 18, all routers have a single IP address on each interface,
   and both the 1-hop and 2-hop neighbors have two interfaces.
   Furthermore, there are now two physical links between routers B and
   C, over distinct interface pairs.

         __________ __________
        |          |          |
       {1}        {2}        {3}                      +-----+   +----{3}
        |          |          |             {1}-------| {2} |---+
     +--'--+    +--'--+    +-----+                    | {5} |   +----{4}
     |  A  |    |  B  |    |  C  |                    +-----+
     +-----+    +-----+    +-----+
                   |          |
                  {5}        {4}
                   |__________|

    Figure 18: Single Addresses, with 1-Hop and 2-Hop Neighbors B and C
    Having Two Interfaces (Left), and Corresponding NHDP Representation
                                  (Right)

   The Local Information Base is identical to that in Example 1.

   The Link Set is identical to that in Example 6, and the 2-Hop Set
   contains, as in Example 5 (and similarly to Examples 3 and 4), two
   2-Hop Tuples representing the two links between routers B and C.

   Note that router A does not have information describing which of
   router B's interfaces is connected to which interfaces of router C,
   or even that the interfaces with addresses {3} and {4} are interfaces
   of the same router.  However, router A knows that the addresses {3}
   and {4} (and thus router C) are reachable using {2} as next hop.








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F.8.  Example 8: Dual Interface Locally and on 1-Hop Neighbor

   In Figure 19, all routers have a single IP address on each interface,
   and both A and its the 1-hop neighbor B have two interfaces.
   Furthermore, there are now two physical links between routers A and
   B, over distinct interface pairs.

         __________ __________
        |          |          |                       +-----+
       {1}        {2}        {3}            {1}-------| {2} |--------{3}
        |          |          |                       | {5} |
     +--'--+    +--'--+    +-----+                    +-----+
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+                    +-----+
        |          |                                  | {2} |
       {6}        {5}                       {6}-------| {5} |--------{3}
        |__________|                                  +-----+

   Figure 19: Single Addresses, with Both A and 1-Hop Neighbor B Having
   Two Interfaces (Left), and Corresponding NHDP Representation (Right)

   The Local Information Set contains two Local Interface Tuples, with
   I_local_iface_addr_list of {1} and {6}, respectively.

   Each Interface Information Base's Link Set contains one Link Tuple,
   representing the links between {1} and {2}, and between {6} and {5},
   respectively.  The 2-Hop Set for interface {1} contains a single
   2-Hop Tuple, with N2_neighbor_iface_addr_list being {2} and
   N2_2hop_addr being {3}.  The 2-Hop Set for interface {6} contains a
   single 2-Hop Tuple, with N2_neighbor_iface_addr_list being {5} and
   N2_2hop_addr being {3}.

   The Neighbor Information Base contains a Neighbor Set containing a
   single Neighbor Tuple, which represents router B, with
   N_neighbor_addr_list being {2,5}.  This entry is denoted by boxing
   {2} with {5}.















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F.9.  Example 9: Dual Interface on All Routers

   In Figure 20, all routers have a single IP address on each interface,
   and all routers have two interfaces.  Furthermore, there are now two
   physical links between A and B, over distinct interface pairs, and
   two physical links between B and C, also over distinct interface
   pairs.

         __________ __________
        |          |          |                       +-----+   +----{3}
       {1}        {2}        {3}            {1}-------| {2} |---+
        |          |          |                       | {5} |   +----{4}
     +--'--+    +--'--+    +-----+                    +-----+
     |  A  |    |  B  |    |  C  |
     +-----+    +-----+    +-----+                    +-----+
        |          |          |                       | {2} |   +----{3}
       {6}        {5}        {4}            {6}-------| {5} |---+
        |__________|__________|                       +-----+   +----{4}

    Figure 20: Single Addresses, with All Routers Having Two Interfaces
           (Left), and Corresponding NHDP Representation (Right)

   The Local Information Set is identical to that in Example 8.  The
   Interface Information Base for each interface in A is also identical
   to that in Example 8, except that an additional 2-Hop Tuple is
   present in each 2-Hop Set, each representing the link between router
   B and the interface of router C with address {4}.

   As in Example 7, router A does not have information describing which
   of router B's interfaces is connected to which interface of C, or
   even that the interfaces with addresses {3} and {4} are interfaces of
   the same router.  However, router A knows that the addresses {3} and
   {4} (and router C) are reachable by using {2} or {5} (depending on
   via which of its local interfaces) as next hop.

















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F.10.  Example 10: Dual Addressed Dual Interfaces on All Routers

   In Figure 21, all routers have two IP addresses on each interface,
   and all routers have two interfaces.  Furthermore, there are now two
   physical links between A and B, over distinct interface pairs, and
   two physical links between B and C, also over distinct interface
   pairs.

                                                                 +--{9}
         __________ __________                            +------|
        |          |          |                 +-----+   |      +--{10}
      {1,2}      {5,6}      {9,10}       {1,2}--|{5,6}|---+
        |          |          |                 |{7,8}|   |      +--{11}
     +--'--+    +--'--+    +-----+              +-----+   +------|
     |  A  |    |  B  |    |  C  |                               +--{12}
     +-----+    +-----+    +-----+
        |          |          |                                  +--{9}
        |          |          |                 +-----+   +------|
        |          |          |                 |{5,6}|   |      +--{10}
      {3,4}      {7,8}     {11,12}       {3,4}--|{7,8}|---+
        |__________|__________|                 +-----+   |      +--{11}
                                                          +------|
                                                                 +--{12}

     Figure 21: Dual Addresses, with All Routers Having Two Interfaces
           (Left) and Corresponding NHDP Representation (Right)

   This example is the combination of all the preceding examples in this
   appendix.  The Local Information Set in A contains Local Information
   Tuples for each of its interfaces, and each Interface Information
   Base contains in its Link Set a representation of links {1,2}-{5,6}
   or {3,4}-{7,8}, respectively.  The Neighbor Set (in the Neighbor
   Information Base) records the existence of router B and all of its
   addresses on all its interfaces, i.e., {5,6,7,8}.

   As in Example 9, each interface address of router C is represented in
   the 2-Hop Set of each Interface Information Base as a link from
   router B to each of these addresses.  Router A does not have
   information describing which of router B's interfaces is connected to
   which interface of C, nor that the addresses {9}, {10}, {11}, and
   {12} are addresses of the same router (or that some of these, such as
   {9} and {10}, are addresses on the same interface of the router).









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F.11.  Example 11: Single Addressed Dual Interface Locally

   In Figure 22, all routers have a single interface, except for router
   A which has two.  Each of A's two interfaces has a link with the
   single interface of router B.  All interfaces have a single address.

         __________ __________
        |     _____|          |
       {1}   |    {2}        {3}             {1}--------{2}---------{3}
        |    |     |          |
     +--'--+ |  +--'--+    +-----+
     |  A  | |  |  B  |    |  C  |
     +-----+ |  +-----+    +-----+
        |    |
       {6}   |                               {6}--------{2}---------{3}
        |____|

      Figure 22: Single Addresses, with A Having Two Interfaces, Both
    Linked to the Single Interface of B (Left), and Corresponding NHDP
                          Representation (Right)

   This is similar to Example 8, except that the single address {2} also
   replaces the address {5}.  In particular, both Link Tuples (one in
   each Link Set, each in its corresponding Interface Information Base)
   have L_neighbor_iface_addr_list being {2}, the Neighbor Set (in the
   Neighbor Information Base) contains a single Neighbor Tuple with
   N_neighbor_addr_list being {2}, and both 2-Hop Tuples (one in each
   2-Hop Set, each in its corresponding Interface Information Base) have
   N2_neighbor_iface_addr_list being {2} and N2_2hop_addr being {3}.






















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RFC 6130                       MANET-NHDP                     April 2011


Authors' Addresses

   Thomas Heide Clausen
   LIX, Ecole Polytechnique

   Phone: +33 6 6058 9349
   EMail: T.Clausen@computer.org
   URI:   http://www.ThomasClausen.org/


   Christopher Dearlove
   BAE Systems ATC

   Phone: +44 1245 242194
   EMail: chris.dearlove@baesystems.com
   URI:   http://www.baesystems.com/


   Justin W. Dean
   Naval Research Laboratory

   Phone: +1 202 767 3397
   EMail: jdean@itd.nrl.navy.mil
   URI:   http://pf.itd.nrl.navy.mil/



























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