





Internet Engineering Task Force (IETF)                         P. Yegani
Request for Comments: 6245                              Juniper Networks
Category: Standards Track                                       K. Leung
ISSN: 2070-1721                                            Cisco Systems
                                                                 A. Lior
                                                     Bridgewater Systems
                                                            K. Chowdhury
                                                               J. Navali
                                                           Cisco Systems
                                                                May 2011


   Generic Routing Encapsulation (GRE) Key Extension for Mobile IPv4

Abstract

   The Generic Routing Encapsulation (GRE) specification contains a Key
   field, which MAY contain a value that is used to identify a
   particular GRE data stream.  This specification defines a new Mobile
   IP extension that is used to exchange the value to be used in the GRE
   Key field.  This extension further allows the Mobility Agents to set
   up the necessary protocol interfaces prior to receiving the mobile
   node traffic.  The new extension allows a Foreign Agent to request
   GRE tunneling without disturbing the Home Agent behavior specified
   for Mobile IPv4.  GRE tunneling with the Key field allows the
   operators to have home networks that consist of multiple Virtual
   Private Networks (VPNs), which may have overlapping home addresses.
   When the tuple <Care of Address, Home Address, and Home Agent
   Address> is the same across multiple subscriber sessions, GRE
   tunneling will provide a means for the Foreign Agent and Home Agent
   to identify data streams for the individual sessions based on the GRE
   key.  In the absence of this key identifier, the data streams cannot
   be distinguished from each other -- a significant drawback when using
   IP-in-IP tunneling.

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/rfc6245.



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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.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. GRE Key Extension ...............................................3
   4. Operation and Use of the GRE Key Extension ......................3
      4.1. Foreign Agent Requirements for GRE Tunneling Support .......3
      4.2. Home Agent Requirements for GRE Tunneling Support ..........4
      4.3. Mobile Node Requirements for GRE Tunneling Support .........5
   5. GRE Key Extension and Tunneling Procedures ......................5
   6. IANA Considerations .............................................6
   7. Security Considerations .........................................6
   8. Acknowledgements ................................................7
   9. Normative References ............................................7

1.  Introduction

   This document specifies a new extension for use by a Foreign Agent
   (FA) operating Mobile IP for IPv4.  The new extension allows a
   Foreign Agent to request Generic Routing Encapsulation (GRE)
   [RFC2784] tunneling without disturbing the Home Agent (HA) behavior
   specified for Mobile IPv4 [RFC5944].  This extension contains the GRE
   key [RFC2890] required for establishing a GRE tunnel between the FA
   and the HA.

   GRE tunneling with the Key field allows the operators to have home
   networks that consist of multiple Virtual Private Networks (VPNs),
   which may have overlapping home addresses.  When the tuple <Care of
   Address, Home Address, and Home Agent Address> is the same across







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   multiple subscriber sessions, GRE tunneling will provide a means for
   the FA and the HA to identify data streams for the individual
   sessions based on the GRE key.  In the absence of this key
   identifier, the data streams cannot be distinguished from each other
   -- a significant drawback when using IP-in-IP tunneling.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].  Other
   terminology is used as already defined in [RFC5944].

3.  GRE Key Extension

   The format of the GRE Key Extension conforms to the extension format
   specified for Mobile IPv4 [RFC5944].  This extension option is used
   by the Foreign Agent to supply GRE key and other necessary
   information to the Home Agent to establish a GRE tunnel between the
   FA and the HA.

4.  Operation and Use of the GRE Key Extension

4.1.  Foreign Agent Requirements for GRE Tunneling Support

   The FA MUST support IP-in-IP tunneling of datagrams for Mobile IPv4
   [RFC5944].  The FA may support GRE tunneling that can be used, for
   example, to allow for overlapping private home IP addresses
   (Section 4.2.2.5 of [X.S0011-E]).  If the FA is capable of supporting
   GRE encapsulation, it should set the 'G' (GRE encapsulation) bit in
   the Flags field in the Agent Advertisement message sent to the Mobile
   Node (MN) during the Mobile IP session establishment.

   If the MN does not set the 'G' bit, the FA MAY fall back to using
   IP-in-IP encapsulation for the session per [RFC5944].

   If the MN does not set the 'G' bit and does not set the 'D'
   (Decapsulation by mobile node) bit (i.e., the mobile node does not
   request GRE tunneling and is not using a co-located care-of address),
   and the local policy allows the FA to override the 'G' bit setting
   received from the MN, the FA MUST include the GRE Key Extension as
   defined in this memo in the Registration Request (RRQ) that it
   propagates to the HA.  The presence of this extension is a request
   for GRE encapsulation that takes precedence over the setting of the
   'G' bit in the Registration Request.  The FA MUST NOT modify the 'G'
   bit in the Registration Request because it is protected by the
   Mobile-Home Authentication extension.




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   If the FA does not support GRE encapsulation, the FA MUST reset the
   'G' bit in the Agent Advertisement message.  In this case, if the MN
   sets the 'G' bit in the Registration Request message, the FA returns
   a Registration Reply (RRP) message to the MN with code 'requested
   encapsulation unavailable' (72) per [RFC5944].

   If the FA allows GRE encapsulation, and either the MN requested GRE
   encapsulation or local policy dictates using GRE encapsulation for
   the session, and the 'D' bit is not set (i.e., the mobile node is not
   using a co-located care-of address), the FA MUST include the GRE Key
   in the GRE Key Extension in all Mobile IP Registration Requests
   (including initial, renewal, and de-registration requests) before
   forwarding the request to the HA.  The FA may include a GRE key of
   value zero in the GRE Key Extension to signal that the HA assigns GRE
   keys in both directions.  The GRE key assignment in the FA and the HA
   is outside the scope of this memo.

   The GRE Key Extension SHALL follow the format defined in [RFC5944].
   This extension SHALL be added after the MN-HA and MN-FA Challenge and
   MN-AAA (Mobile Node - Authentication, Authorization, and Accounting)
   extensions (if any) and before the FA-HA Auth extension (if any).

4.2.  Home Agent Requirements for GRE Tunneling Support

   The HA MUST follow the procedures specified in [RFC5944] in
   processing this extension in Registration Request messages.

   If the HA receives the GRE Key Extension in a Registration Request
   and does not recognize this non-skippable extension, it MUST silently
   discard the message.  The HA MUST use other alternative forms of
   encapsulation (e.g., IP-in-IP tunneling), when requested by the
   mobile node per [RFC5944].

   If the HA receives the GRE Key Extension in a Registration Request
   and recognizes the GRE Key Extension but is not configured to support
   GRE encapsulation, it MUST send an RRP with code 'requested
   encapsulation unavailable (139)' [RFC3024].

   If the HA receives a Registration Request with a GRE Key Extension
   but without the 'G' bit set, the HA SHOULD treat this as if the 'G'
   bit is set in the Registration Request; i.e., the presence of a GRE
   Key Extension indicates a request for GRE encapsulation.

   If the HA receives the GRE Key Extension in a Registration Request,
   and it recognizes the GRE Key Extension as well as supports GRE
   encapsulation, the following procedures should apply:





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   o  The HA SHOULD accept the RRQ and send an RRP with code
      'registration accepted (0)'.

   o  The HA MUST assign a GRE key and include the GRE Key Extension in
      the RRP before sending it to the FA.

   o  The HA MUST include the GRE Key Extension in all RRPs in response
      to any RRQ that included the GRE Key Extension, when a GRE key is
      available for the registration.

   If the HA receives the GRE Key Extension in the initial Registration
   Request and recognizes the GRE Key Extension carrying a GRE key value
   of zero, it SHOULD accept the RRQ and send an RRP with code
   'registration accepted (0)', and the following procedures apply:

   o  The HA MUST assign GRE keys for both directions and include these
      keys in the GRE Key Extension in the RRP before sending it to
      the FA.

   o  The HA MUST include the GRE Key Extension in the RRP in response
      to the initial RRQ that included the GRE Key Extension, when a GRE
      key is available for the registration.

4.3.  Mobile Node Requirements for GRE Tunneling Support

   If the MN is capable of supporting GRE encapsulation, it SHOULD set
   the 'G' bit in the Flags field in the Registration Request per
   [RFC5944].

5.  GRE Key Extension and Tunneling Procedures

   GRE tunneling support for Mobile IP will permit asymmetric GRE
   keying; i.e., the FA assigns a GRE key for use in encapsulated
   traffic, and the HA can assign its own GRE key.  Once the GRE keys
   have been exchanged, the FA uses the HA-assigned key in the
   encapsulating GRE header for reverse tunneling, and the HA uses the
   FA-assigned key in the encapsulating GRE header.

   The format of the GRE Key Extension is as shown below.

   The GRE Key Extension MAY be included in Registration Requests or
   Registration Replies [RFC5944].  The GRE Key Extension is used to
   inform the recipient of the Mobile IP request of the value to be used
   in the GRE Key field.







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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |   Sub-Type    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Key Identifier                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: GRE Key Extension

   Type

      48 - An 8-bit identifier of the GRE Key Extension type
      (non-skippable)

   Sub-Type

      0

   Length

      4

   Key Identifier

      This is a four-octet value assigned during registration and
      inserted in every GRE packet of the user traffic.

6.  IANA Considerations

   The GRE Key Extension defined in this memo is a Mobile IP extension
   as defined in [RFC5944].  IANA has assigned a Type value (48) for
   this extension from the non-skippable range (0-127).

   The GRE Key Extension introduces a new sub-type numbering space,
   where the value 0 has been assigned from the range 0 to 255.
   Approval of new GRE Key Extension sub-type values is to be made
   through Expert Review with Specification Required.

7.  Security Considerations

   This specification does not introduce any new security
   considerations, beyond those described in [RFC5944].








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   Despite its name, the GRE Key Extension has little to do with
   security.  The word "Key" here is not used in the cryptographic sense
   of a shared secret that must be protected but rather in the sense of
   an "index" or demultiplexing value that can be used to distinguish
   packets belonging to a given flow within a GRE tunnel.

8.  Acknowledgements

   Thanks to Jun Wang, Gopal Dommety, and Sri Gundavelli for their
   helpful comments, offline discussions, and review of the initial
   draft version of this document.  Also, Pete McCann and Simon
   Mizikovsky provided valuable review comments.

9.  Normative References

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

   [RFC2784]    Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
                Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
                March 2000.

   [RFC2890]    Dommety, G., "Key and Sequence Number Extensions to
                GRE", RFC 2890, September 2000.

   [RFC3024]    Montenegro, G., Ed., "Reverse Tunneling for Mobile IP,
                revised", RFC 3024, January 2001.

   [RFC5944]    Perkins, C., Ed., "IP Mobility Support for IPv4,
                Revised", RFC 5944, November 2010.

   [X.S0011-E]  3rd Generation Partnership Project 2, "cdma2000 Wireless
                IP Network Standard: Simple IP and Mobile IP Access
                Services", 3GPP2 X.S0011-002-E Version 1.0,
                November 2009, <http://www.3gpp2.org/Public_html/specs/
                X.S0011-002-E_v1.0_091116.pdf>.















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Authors' Addresses

   Parviz Yegani
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, California  94089
   USA
   Phone: +1 408-759-1973
   EMail: pyegani@juniper.net


   Kent Leung
   Cisco Systems Incorporated
   170 West Tasman Drive
   San Jose, California  95134
   USA
   Phone: +1 408 526 5030
   EMail: kleung@cisco.com


   Avi Lior
   Bridgewater Systems Corporation
   303 Terry Fox Drive
   Ottawa, Ontario  K2K 3J1
   Canada
   Phone: +1 613-591-6655
   EMail: avi@bridgewatersystems.com


   Kuntal Chowdhury
   Cisco Systems Incorporated
   170 West Tasman Drive
   San Jose, California  95134
   USA
   EMail: kchowdhu@cisco.com


   Jay Navali
   Cisco Systems Incorporated
   170 West Tasman Drive
   San Jose, California  95134
   USA
   EMail: jnavali@cisco.com








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