





Internet Engineering Task Force (IETF)                        A. Bierman
Request for Comments: 6243                                       Brocade
Category: Standards Track                                     B. Lengyel
ISSN: 2070-1721                                                 Ericsson
                                                               June 2011


                  With-defaults Capability for NETCONF

Abstract

   The Network Configuration Protocol (NETCONF) defines ways to read and
   edit configuration data from a NETCONF server.  In some cases, part
   of this data may not be set by the NETCONF client, but rather a
   default value known to the server is used instead.  In many
   situations the NETCONF client has a priori knowledge about default
   data, so the NETCONF server does not need to save it in a NETCONF
   configuration datastore or send it to the client in a retrieval
   operation reply.  In other situations the NETCONF client will need
   this data from the server.  Not all server implementations treat this
   default data the same way.  This document defines a capability-based
   extension to the NETCONF protocol that allows the NETCONF client to
   identify how defaults are processed by the server, and also defines
   new mechanisms for client control of server processing of default
   data.

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/rfc6243.












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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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Default-Handling Behavior  . . . . . . . . . . . . . . . .  5
     1.3.  Client Controlled Retrieval of Default Data  . . . . . . .  5
   2.  Default-Handling Basic Modes . . . . . . . . . . . . . . . . .  6
     2.1.  'report-all' Basic Mode  . . . . . . . . . . . . . . . . .  6
       2.1.1.  'report-all' Basic Mode Retrieval  . . . . . . . . . .  6
       2.1.2.  'report-all' <with-defaults> Retrieval . . . . . . . .  6
       2.1.3.  'report-all' <edit-config> and <copy-config>
               Behavior . . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  'trim' Basic Mode  . . . . . . . . . . . . . . . . . . . .  7
       2.2.1.  'trim' Basic Mode Retrieval  . . . . . . . . . . . . .  7
       2.2.2.  'trim' <with-defaults> Retrieval . . . . . . . . . . .  7
       2.2.3.  'trim' <edit-config> and <copy-config> Behavior  . . .  7
     2.3.  'explicit' Basic Mode  . . . . . . . . . . . . . . . . . .  8
       2.3.1.  'explicit' Basic Mode Retrieval  . . . . . . . . . . .  8
       2.3.2.  'explicit' <with-defaults> Retrieval . . . . . . . . .  8
       2.3.3.  'explicit' <edit-config> and <copy-config> Behavior  .  8
   3.  Retrieval of Default Data  . . . . . . . . . . . . . . . . . .  9
     3.1.  'report-all' Retrieval Mode  . . . . . . . . . . . . . . .  9
     3.2.  'trim' Retrieval Mode  . . . . . . . . . . . . . . . . . .  9
     3.3.  'explicit' Retrieval Mode  . . . . . . . . . . . . . . . .  9
     3.4.  'report-all-tagged' Retrieval Mode . . . . . . . . . . . .  9
   4.  With-defaults Capability . . . . . . . . . . . . . . . . . . . 10
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.2.  Dependencies . . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Capability Identifier  . . . . . . . . . . . . . . . . . . 10
     4.4.  New Operations . . . . . . . . . . . . . . . . . . . . . . 11
     4.5.  Modifications to Existing Operations . . . . . . . . . . . 11
       4.5.1.  <get>, <get-config>, and <copy-config> Operations  . . 11
       4.5.2.  <edit-config> Operation  . . . . . . . . . . . . . . . 12



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       4.5.3.  Other Operations . . . . . . . . . . . . . . . . . . . 13
     4.6.  Interactions with Other Capabilities . . . . . . . . . . . 13
   5.  YANG Module for the <with-defaults> Parameter  . . . . . . . . 13
   6.  XSD for the 'default' Attribute  . . . . . . . . . . . . . . . 17
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 19
   Appendix A.  Usage Examples  . . . . . . . . . . . . . . . . . . . 20
     A.1.  Example YANG Module  . . . . . . . . . . . . . . . . . . . 20
     A.2.  Example Data Set . . . . . . . . . . . . . . . . . . . . . 21
     A.3.  Protocol Operation Examples  . . . . . . . . . . . . . . . 22
       A.3.1.  <with-defaults> = 'report-all' . . . . . . . . . . . . 22
       A.3.2.  <with-defaults> = 'report-all-tagged'  . . . . . . . . 23
       A.3.3.  <with-defaults> = 'trim' . . . . . . . . . . . . . . . 24
       A.3.4.  <with-defaults> = 'explicit' . . . . . . . . . . . . . 25

1.  Introduction

   The NETCONF protocol [RFC6241] defines ways to read configuration and
   state data from a NETCONF server.  Part of the configuration data may
   not be set by the NETCONF client, but rather by a default value from
   the data model.  In many situations the NETCONF client has a priori
   knowledge about default data, so the NETCONF server does not need to
   send it to the client.  A priori knowledge can be obtained, e.g.,
   from a document formally describing the data models supported by the
   NETCONF server.

   It can be important for a client to know exactly how a server
   implementation will handle default data.  There are subtle
   differences in some protocol operations where the default-handling
   behavior of the server will affect the outcome of the operation.

1.1.  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].

   Data model schema:  A document or set of documents describing the
      data models supported by the NETCONF server.

   Management application:  A computer program running outside the
      NETCONF server that configures or supervises the NETCONF server.
      A management application can reach the device, e.g., via NETCONF,
      command line interface (CLI), or the Simple Network Management
      Protocol (SNMP).




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   Schema default data:  Data specified in the data model schema as
      default, that is, set or used by the device whenever the NETCONF
      client or other management application/user does not provide a
      specific value for the relevant data node.  Schema default data
      may or may not be stored as part of a configuration datastore,
      depending on the basic mode used by a particular server.

   Default data:  Conceptual data containing a default value.  Default
      data is not kept in a datastore.  Not all servers use the same
      criteria to decide if a data node is actually instantiated in a
      datastore.  If a data node is not present in a datastore, and a
      schema default definition is in use by the server instead, then it
      is considered to be a default data node.

   Default value:  A default value is a value for a data node instance
      that is conceptually in use by the server, when the data node
      instance does not exist.

   Explicitly set data:  Data that is set to any value by a NETCONF
      client or other management application by the way of an explicit
      management operation, including any data model schema default
      value.  Any value set by the NETCONF server that is not the schema
      defined default value is also considered explicitly set data.

   <with-defaults> retrieval:  Refers to a protocol operation that
      includes the <with-default> parameter to control the handling of
      default data.

   :with-defaults:  The shorthand notation for the with-defaults
      capability identifier.

   The following terms are defined in [RFC6241]:

   o  client

   o  datastore

   o  operation

   o  server

   The following term is defined in [RFC6020]:

   o  data node







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1.2.  Default-Handling Behavior

   The default-handling behavior used by a server will impact NETCONF
   protocol operations in two ways:

   1.  Data retrieval: A server is normally allowed to exclude data
       nodes that it considers to contain the default value.  The actual
       nodes omitted depend on the default-handling behavior used by the
       server.

   2.  Create and delete operations: The <edit-config> 'operation'
       attribute can be used to create and/or delete specific data
       nodes.  These operations depend on whether or not the target node
       currently exists.  The server's default-handling behavior will
       determine whether or not the requested node currently exists in
       the configuration datastore.

1.3.  Client Controlled Retrieval of Default Data

   A networking device may have a large number of default values.  Often
   the default values are specifically defined with a reasonable value,
   documented and well-known, so that the management user does not need
   to handle them.  For these reasons, it is quite common for networking
   devices to suppress the output of parameters having the default
   value.

   However, there are use-cases when a NETCONF client will need the
   default data from the server:

   o  The management application often needs a single, definitive, and
      complete set of configuration values that determine how the
      networking device works.

   o  Documentation about default values can be unreliable or
      unavailable.

   o  Some management applications might not have the capabilities to
      correctly parse and interpret formal data models.

   o  Human users might want to understand the received data without
      consultation of the documentation.

   In all these cases, the NETCONF client will need a mechanism to
   retrieve default data from a NETCONF server.

   This document defines a NETCONF protocol capability to identify the
   server's default-handling behavior, an XML
   [W3C.REC-xmlschema-0-20041028] attribute to identify default data,



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   and a YANG module extension to the NETCONF protocol that allows the
   NETCONF client to control whether default data is returned by the
   server.

2.  Default-Handling Basic Modes

   Not all server implementations treat default data in the same way.
   Instead of forcing a single implementation strategy, this document
   allows a server to advertise a particular style of default-handling,
   and the client can adjust accordingly.  Client implementations are
   expected to be powerful enough to support all three of the server
   basic default-handling modes.

   NETCONF servers report default data in different ways.  This document
   specifies three standard default-handling basic modes that a server
   implementer may choose from:

   o  report-all

   o  trim

   o  explicit

   A server MUST select one of the three basic modes defined in this
   section for handling default data.

2.1.  'report-all' Basic Mode

   A server that uses the 'report-all' basic mode does not consider any
   data node to be default data, even schema default data.

2.1.1.  'report-all' Basic Mode Retrieval

   When data is retrieved from a server using the 'report-all' basic
   mode, and the <with-defaults> parameter is not present, all data
   nodes MUST be reported.

2.1.2.  'report-all' <with-defaults> Retrieval

   If the 'report-all' basic mode is used by the server, then the server
   MUST support the <with-defaults> parameter with a value equal to
   'report-all', as specified in Section 3.1.

2.1.3.  'report-all' <edit-config> and <copy-config> Behavior

   The server MUST consider every data node to exist, even those
   containing a schema default value.  A valid 'create' operation
   attribute for a data node that contains its schema default value MUST



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   fail with a 'data-exists' error-tag.  A valid 'delete' operation
   attribute for a data node that contains its schema default value MUST
   succeed, even though the data node is immediately replaced by the
   server with the default value.

   A server that uses the 'report-all' basic mode has no concept of a
   default node, so the 'report-all-tagged' <with-defaults> retrieval
   mode is not relevant.  There will never be any tagged nodes, since
   there are no nodes that are omitted in a basic-mode retrieval
   operation.  If the 'default' attribute is present in any
   configuration data, the server MUST return an <rpc-error> response
   with an 'unknown-attribute' error-tag.

2.2.  'trim' Basic Mode

   A server that uses the 'trim' basic mode MUST consider any data node
   set to its schema default value to be default data.

2.2.1.  'trim' Basic Mode Retrieval

   When data is retrieved from a server using the 'trim' basic mode, and
   the <with-defaults> parameter is not present, data nodes MUST NOT be
   reported if they contain the schema default value.  Non-configuration
   data nodes containing the schema default value MUST NOT be reported.

2.2.2.  'trim' <with-defaults> Retrieval

   If the 'trim' basic mode is used by the server, then the server MUST
   support the <with-defaults> parameter with a value equal to 'trim',
   as specified in Section 3.2.

2.2.3.  'trim' <edit-config> and <copy-config> Behavior

   The server MUST consider any data node that does not contain its
   schema default value to exist.  A valid 'create' operation attribute
   for a data node that has a schema default value defined MUST succeed.
   A valid 'delete' operation attribute for a missing data node that has
   a schema default value MUST fail.  The server MUST return an
   <rpc-error> response with a 'data-missing' error-tag.

   If a client sets a data node to its schema default value, using any
   valid operation, it MUST succeed, although the data node MUST NOT be
   saved in the NETCONF configuration datastore.  This has the same
   effect as removing the data node and treating it as default data.

   If the server supports the 'report-all-tagged' value for the
   <with-defaults> parameter, then the 'default' attribute MUST be




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   accepted in configuration input, as described in Section 4.5.1 and
   Section 4.5.2.

2.3.  'explicit' Basic Mode

   A server that uses the 'explicit' basic mode MUST consider any data
   node that is not explicitly set data to be default data.

2.3.1.  'explicit' Basic Mode Retrieval

   When data is retrieved from a server using the 'explicit' basic mode,
   and the <with-defaults> parameter is not present, data nodes MUST be
   reported if explicitly set by the client, even if they contain the
   schema default value.  Non-configuration data nodes containing the
   schema default value MUST be reported.

2.3.2.  'explicit' <with-defaults> Retrieval

   If the 'explicit' basic mode is used by the server, the server MUST
   support the <with-defaults> parameter with a value equal to
   'explicit', as specified in Section 3.3.

2.3.3.  'explicit' <edit-config> and <copy-config> Behavior

   The server considers any data node that is explicitly set data to
   exist.  A valid 'create' operation attribute for a data node that has
   been set by a client to its schema default value MUST fail with a
   'data-exists' error-tag.  A valid 'create' operation attribute for a
   data node that has been set by the server to its schema default value
   MUST succeed.  A valid 'delete' operation attribute for a data node
   that has been set by a client to its schema default value MUST
   succeed.  A valid 'delete' operation attribute for a data node that
   has been set by the server to its schema default value MUST fail with
   a 'data-missing' error-tag.

   If the server supports the 'report-all-tagged' retrieval mode in its
   :with-defaults capability, then the 'default' attribute MUST be
   accepted in configuration input.  If all NETCONF <edit-config> or
   <copy-config> parameters are valid, then the server will treat a
   tagged data node (i.e., the 'default' attribute set to 'true' or '1')
   as a request to return that node to default data.  If this request is
   valid within the context of the requested NETCONF operation, then the
   data node is removed and returned to its default value.  The data
   node within the NETCONF message MUST contain a value in this case,
   which MUST be equal to the schema default value.  If not, the server
   MUST return an <rpc-error> response with an 'invalid-value' error-
   tag.




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3.  Retrieval of Default Data

   This document defines a new parameter, called <with-defaults>, which
   can be added to specific NETCONF operation request messages to
   control how retrieval of default data is treated by the server.

   A server that implements this specification MUST accept the
   <with-defaults> parameter containing the enumeration for any of the
   default-handling modes it supports.  The <with-defaults> parameter
   contains one of the four enumerations defined in this section.

3.1.  'report-all' Retrieval Mode

   When data is retrieved with a <with-defaults> parameter equal to
   'report-all', all data nodes MUST be reported, including any data
   nodes considered to be default data by the server.

3.2.  'trim' Retrieval Mode

   When data is retrieved with a <with-defaults> parameter equal to
   'trim', data nodes MUST NOT be reported if they contain the schema
   default value.  Non-configuration data nodes containing the schema
   default value MUST NOT be reported.

3.3.  'explicit' Retrieval Mode

   When data is retrieved with a <with-defaults> parameter equal to
   'explicit', a data node that was set by a client to its schema
   default value MUST be reported.  A conceptual data node that would be
   set by the server to the schema default value MUST NOT be reported.
   Non-configuration data nodes containing the schema default value MUST
   be reported.

3.4.  'report-all-tagged' Retrieval Mode

   In addition to the basic modes, a special variant of the 'report-all'
   basic mode is available called 'report-all-tagged'.  This mode MUST
   be supported on a server if the 'also-supported' parameter in the
   :with-defaults capability contains the 'report-all-tagged' option.
   Refer to Section 4 for encoding details for this capability.

   In this mode the server returns all data nodes, just like the
   'report-all' mode, except a data node that is considered by the
   server to contain default data will include an XML attribute to
   indicate this condition.  This is useful for an application to
   determine which nodes are considered to contain default data by the
   server, within a single retrieval operation.




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   A server that supports 'report-all-tagged' MUST also accept the
   'default' XML attribute within configuration input to the
   <edit-config> or <copy-config> operations.  Refer to Section 6 for
   XML encoding details of the 'default' XML attribute.

4.  With-defaults Capability

4.1.  Overview

   The :with-defaults capability indicates which default-handling basic
   mode is supported by the server.  It may also indicate support for
   additional defaults retrieval modes.  These retrieval modes allow a
   NETCONF client to control whether default data is returned by the
   server.  The capability affects both configuration and state data
   (while acknowledging that the usage of default values for state data
   is less prevalent).  Sending of default data is controlled for each
   individual operation separately.

   A NETCONF server implementing the :with-defaults capability:

   o  MUST indicate its basic mode behavior by including the 'basic-
      mode' parameter in the capability URI, as defined in Section 4.3.

   o  MUST support the YANG module defined in Section 5 for the default-
      handling mode indicated by the 'basic-mode' parameter.

   o  SHOULD support the YANG module in Section 5 for the default-
      handling mode identified by the 'report-all' or 'report-all-
      tagged' enumeration value.

   o  If the 'report-all-tagged' default-handling mode is supported,
      then the 'default' attribute MUST be supported.

   o  MAY support the YANG module in Section 5 for additional default-
      handling modes.

4.2.  Dependencies

   None.

4.3.  Capability Identifier

   urn:ietf:params:netconf:capability:with-defaults:1.0

   The identifier MUST have a parameter: "basic-mode".  This indicates
   how the server will treat default data, as defined in Section 2.  The
   allowed values of this parameter are 'report-all', 'trim', and
   'explicit', as defined in Section 2.



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   The identifier MAY have another parameter: "also-supported".  This
   parameter indicates which additional enumeration values (besides the
   basic-mode enumeration) the server will accept for the
   <with-defaults> parameter in Section 5.  The value of the parameter
   is a comma-separated list of one or more modes that are supported
   besides the mode indicated in the 'basic-mode' parameter.  Possible
   modes are 'report-all', 'report-all-tagged', 'trim', and 'explicit',
   as defined in Section 3.

   Note that this protocol capability URI is separate from the YANG
   module capability URI for the YANG module in Section 5.  A server
   that implements this module MUST also advertise a YANG module
   capability URI according to the rules specified in [RFC6020].

   Examples:

   urn:ietf:params:netconf:capability:with-defaults:1.0?basic-
   mode=explicit

   urn:ietf:params:netconf:capability:with-defaults:1.0?basic-
   mode=explicit&also-supported=report-all,report-all-tagged

4.4.  New Operations

   None.

4.5.  Modifications to Existing Operations

4.5.1.  <get>, <get-config>, and <copy-config> Operations

   A new <with-defaults> XML element is added to the input for the
   <get>, <get-config>, and <copy-config> operations.  If the
   <with-defaults> element is present, it controls the reporting of
   default data.  The server MUST return default data in the NETCONF
   <rpc-reply> messages according to the value of this element, if the
   server supports the specified retrieval mode.

   This parameter only controls these specified retrieval operations,
   and does not impact any other operations or the non-volatile storage
   of configuration data.

   The <with-defaults> element is defined in the XML namespace for the
   ietf-netconf-with-defaults.yang module in Section 5, not the XML
   namespace for the <get>, <get-config>, and <copy-config> operations.

   Allowed values of the with-defaults element are taken from the 'with-
   defaults-type' typedef in Section 5.  The allowed values for a
   particular server are restricted to the values that the server



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   indicates it supports within the :with-defaults capability, in the
   'basic-mode' and 'also-supported' parameters.

   If an unsupported value is used, the NETCONF server MUST return an
   <rpc-error> response with an 'invalid-value' error-tag.

   If the <with-defaults> element is not present, the server MUST follow
   its basic mode behavior as indicated by the :with-defaults capability
   identifier's 'basic-mode' parameter, defined in Section 4.3.

   The <get> and <get-config> operations support a separate filtering
   mechanism, using the <filter> parameter.  The defaults filtering is
   conceptually done before the <filter> parameter is processed.  For
   example, if the <with-defaults> parameter is equal to 'report-all',
   then the <filter> parameter is conceptually applied to all data nodes
   and all default data.

   The <copy-config> operation is only affected by the <with-defaults>
   parameter if the target of the operation is specified with the <url>
   parameter.  If the target is a NETCONF configuration datastore (i.e.,
   running, candidate, or startup), the <with-defaults> parameter has no
   effect.  The server MUST use its basic mode when copying data to a
   NETCONF configuration datastore.  If the <with-defaults> parameter is
   present in this case, it MUST be silently ignored by the server.

   If the server supports the 'report-all-tagged' mode, then the
   'default' attribute defined in Section 6 also impacts the
   <copy-config> operation.  If the 'default' attribute is present and
   set to 'true' or '1', then the server MUST treat the new data node as
   a request to return that node to its default value (i.e., remove it
   from the configuration datastore).  The data node within the NETCONF
   message MUST contain a value in this case, which MUST be equal to the
   schema default value.  If not, the server MUST return an <rpc-error>
   response with an 'invalid-value' error-tag.

4.5.2.  <edit-config> Operation

   The <edit-config> operation has several editing modes.  The 'create'
   and 'delete' editing operations are affected by the default-handling
   basic mode.  The other enumeration values for the NETCONF operation
   attribute are not affected.

   If the operation attribute contains the value 'create', and the data
   node already exists in the target configuration datastore, then the
   server MUST return an <rpc-error> response with an 'invalid-value'
   error-tag.





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   If the client sets a data node to its schema default value, the
   server MUST accept the request if it is valid.  The server MUST keep
   or discard the new value based on its default-handling basic mode.
   For the 'trim' basic mode, all schema default values are discarded;
   otherwise, a client-provided schema default value is saved in a
   NETCONF configuration datastore.

   If the server supports the 'report-all-tagged' mode, then the
   'default' attribute defined in Section 6 also impacts the
   <edit-config> operation.  If the 'default' attribute is present and
   set to 'true' or '1', then the server MUST treat the new data node as
   a request to return that node to its default value (i.e., remove it
   from the configuration datastore).  The data node within the NETCONF
   message MUST contain a value in this case, which MUST be equal to the
   schema default value.  If not, the server MUST return an <rpc-error>
   response with an 'invalid-value' error-tag.

   If the 'default' attribute is present, then the effective operation
   for the target data node MUST be 'create', 'merge', or 'replace'.  If
   not, then the server MUST return an <rpc-error> response with an
   'invalid-value' error-tag.  For example, if 'create' is the effective
   operation, then the create request must be valid on its own (e.g.,
   current data node MUST NOT exist).  The procedure for determining the
   effective operation is defined in [RFC6241].  It is derived from the
   'default-operation' parameter and/or any operation attributes that
   are present in the data node or any of its ancestor nodes, within the
   <edit-config> request.

4.5.3.  Other Operations

   Other operations that return configuration data SHOULD also handle
   default data according to the rules set in this document, and
   explicitly state this in their documentation.  If this is not
   specified in the document defining the respective operation, the
   default-handling rules described herein do not affect these
   operations.

4.6.  Interactions with Other Capabilities

   None.

5.  YANG Module for the <with-defaults> Parameter

   The following YANG module defines the addition of the with-defaults
   element to the <get>, <get-config>, and <copy-config> operations.
   The YANG language is defined in [RFC6020].  The above operations are
   defined in YANG in [RFC6241].  Every NETCONF server that supports the
   :with-defaults capability MUST implement this YANG module.



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  <CODE BEGINS> file="ietf-netconf-with-defaults@2011-06-01.yang"

  module ietf-netconf-with-defaults {

     namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults";

     prefix ncwd;

     import ietf-netconf { prefix nc; }

     organization
      "IETF NETCONF (Network Configuration Protocol) Working Group";

     contact
      "WG Web:   <http://tools.ietf.org/wg/netconf/>

       WG List:  <netconf@ietf.org>

       WG Chair: Bert Wijnen
                 <bertietf@bwijnen.net>

       WG Chair: Mehmet Ersue
                 <mehmet.ersue@nsn.com>

       Editor: Andy Bierman
               <andy.bierman@brocade.com>

       Editor: Balazs Lengyel
               <balazs.lengyel@ericsson.com>";

     description
      "This module defines an extension to the NETCONF protocol
       that allows the NETCONF client to control how default
       values are handled by the server in particular NETCONF
       operations.

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

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject
       to the license terms contained in, the Simplified BSD License
       set forth in Section 4.c of the IETF Trust's Legal Provisions
       Relating to IETF Documents
       (http://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC 6243; see
       the RFC itself for full legal notices.";



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     revision 2011-06-01 {
       description
         "Initial version.";
       reference
        "RFC 6243: With-defaults Capability for NETCONF";
     }

     typedef with-defaults-mode {
        description
          "Possible modes to report default data.";
        reference
           "RFC 6243; Section 3.";
        type enumeration {
           enum report-all {
               description
                 "All default data is reported.";
               reference
                 "RFC 6243; Section 3.1";
           }
           enum report-all-tagged {
               description
                 "All default data is reported.
                  Any nodes considered to be default data
                  will contain a 'default' XML attribute,
                  set to 'true' or '1'.";
               reference
                 "RFC 6243; Section 3.4";
           }
           enum trim {
               description
                 "Values are not reported if they contain the default.";
               reference
                 "RFC 6243; Section 3.2";
           }
           enum explicit {
               description
                 "Report values that contain the definition of
                  explicitly set data.";
               reference
                 "RFC 6243; Section 3.3";
           }
       }
     }

     grouping with-defaults-parameters {
       description
         "Contains the <with-defaults> parameter for control
          of defaults in NETCONF retrieval operations.";



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       leaf with-defaults {
         description
           "The explicit defaults processing mode requested.";
         reference
           "RFC 6243; Section 4.5.1";

         type with-defaults-mode;
       }
     }

     // extending the get-config operation
     augment /nc:get-config/nc:input {
         description
           "Adds the <with-defaults> parameter to the
            input of the NETCONF <get-config> operation.";
         reference
           "RFC 6243; Section 4.5.1";

         uses with-defaults-parameters;
     }

     // extending the get operation
     augment /nc:get/nc:input {
         description
           "Adds the <with-defaults> parameter to
            the input of the NETCONF <get> operation.";
         reference
           "RFC 6243; Section 4.5.1";

         uses with-defaults-parameters;
     }

     // extending the copy-config operation
     augment /nc:copy-config/nc:input {
         description
           "Adds the <with-defaults> parameter to
            the input of the NETCONF <copy-config> operation.";
         reference
           "RFC 6243; Section 4.5.1";

         uses with-defaults-parameters;
     }

  }

  <CODE ENDS>





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6.  XSD for the 'default' Attribute

   The following XML Schema document [W3C.REC-xml-20081126] defines the
   'default' attribute, described within this document.  This XSD is
   only relevant if the server supports the 'report-all-tagged' defaults
   retrieval mode.

   The 'default' attribute uses the XSD data type 'boolean'.  In
   accordance with Section 3.2.2.1 of XML Schema Part 2: Datatypes, the
   allowable lexical representations for the xs:boolean datatype are the
   strings "0" and "false" for the concept of false and the strings "1"
   and "true" for the concept of true.  Implementations MUST support
   both styles of lexical representation.

<CODE BEGINS> file="defaults.xsd"

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns="urn:ietf:params:xml:ns:netconf:default:1.0"
           targetNamespace="urn:ietf:params:xml:ns:netconf:default:1.0"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified"
           xml:lang="en">

  <xs:annotation>
    <xs:documentation>
      This schema defines the syntax for the 'default' attribute
      described within this document.
    </xs:documentation>
  </xs:annotation>

  <!--
    default attribute
    -->
  <xs:attribute name="default" type="xs:boolean" default="false">
    <xs:annotation>
      <xs:documentation>
        This attribute indicates whether the data node represented
        by the XML element containing this attribute is considered
        by the server to be default data.  If set to 'true' or '1', then
        the data node is default data.  If 'false' or '0', then the
        data node is not default data.
      </xs:documentation>
    </xs:annotation>
  </xs:attribute>






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</xs:schema>

<CODE ENDS>

7.  IANA Considerations

   This document registers the following capability identifier URN in
   the 'Network Configuration Protocol (NETCONF) Capability URNs'
   registry:

      urn:ietf:params:netconf:capability:with-defaults:1.0

   This document registers two XML namespace URNs in the 'IETF XML
   registry', following the format defined in [RFC3688].

      URI: urn:ietf:params:xml:ns:netconf:default:1.0

      URI: urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults

   Registrant Contact: The NETCONF WG of the IETF.

   XML: N/A, the requested URIs are XML namespaces.

   This document registers one module name in the 'YANG Module Names'
   registry, defined in [RFC6020] .

      name: ietf-netconf-with-defaults

      prefix: ncwd

      namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults

      RFC: 6243

8.  Security Considerations

   This document defines an extension to existing NETCONF protocol
   operations.  It does not introduce any new or increased security
   risks into the management system.

   The 'with-defaults' capability gives clients control over the
   retrieval of default data from a NETCONF datastore.  The security
   consideration of [RFC6241] applies to this document as well.








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9.  Acknowledgements

   Thanks to Martin Bjorklund, Sharon Chisholm, Phil Shafer, Juergen
   Schoenwaelder, Kent Watsen, Washam Fan, and many other members of the
   NETCONF WG for providing important input to this document.

10.  Normative References

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

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A.  Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, June 2011.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

   [W3C.REC-xmlschema-0-20041028]
              Fallside, D. and P. Walmsley, "XML Schema Part 0: Primer
              Second Edition", World Wide Web Consortium Recommendation
              REC-xmlschema-0-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-0-20041028>.

















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Appendix A.  Usage Examples

A.1.  Example YANG Module

   The following YANG module defines an example interfaces table to
   demonstrate how the <with-defaults> parameter behaves for a specific
   data model.

   Note that this is not a real module, and implementation of this
   module is not required for conformance to the :with-defaults
   capability, defined in Section 4.  This module is not to be
   registered with IANA, and is not considered to be a code component.
   It is intentionally very terse, and includes few descriptive
   statements.


     module example {

     namespace "http://example.com/ns/interfaces";

     prefix exam;

     typedef status-type {
        description "Interface status";
        type enumeration {
          enum ok;
          enum 'waking up';
          enum 'not feeling so good';
          enum 'better check it out';
          enum 'better call for help';
        }
        default ok;
     }

     container interfaces {
         description "Example interfaces group";

         list interface {
           description "Example interface entry";
           key name;

           leaf name {
             description
               "The administrative name of the interface.
                This is an identifier that is only unique
                within the scope of this list, and only
                within a specific server.";
             type string {



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               length "1 .. max";
             }
           }

           leaf mtu {
             description
               "The maximum transmission unit (MTU) value assigned to
                this interface.";
             type uint32;
             default 1500;
           }

           leaf status {
             description
               "The current status of this interface.";
             type status-type;
             config false;
           }
         }
       }
     }

A.2.  Example Data Set

   The following data element shows the conceptual contents of the
   example server for the protocol operation examples in the next
   section.  This includes all the configuration data nodes, non-
   configuration data nodes, and default leafs.

       <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
         <interfaces xmlns="http://example.com/ns/interfaces">
           <interface>
             <name>eth0</name>
             <mtu>8192</mtu>
             <status>up</status>
           </interface>
           <interface>
             <name>eth1</name>
             <mtu>1500</mtu>
             <status>up</status>
           </interface>
           <interface>
             <name>eth2</name>
             <mtu>9000</mtu>
             <status>not feeling so good</status>
           </interface>
           <interface>
             <name>eth3</name>



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             <mtu>1500</mtu>
             <status>waking up</status>
           </interface>
         </interfaces>
       </data>

   In this example, the 'mtu' field for each interface entry is set in
   the following manner:

              +--------------+--------------+--------------+
              | name         | set by       | mtu          |
              +--------------+--------------+--------------+
              | eth0         | client       | 8192         |
              | eth1         | server       | 1500         |
              | eth2         | client       | 9000         |
              | eth3         | client       | 1500         |
              +--------------+--------------+--------------+

A.3.  Protocol Operation Examples

   The following examples show some <get> operations using the 'with-
   defaults' element.  The data model used for these examples is defined
   in Appendix A.1.

   The client is retrieving all the data nodes within the 'interfaces'
   object, filtered with the <with-defaults> parameter.

A.3.1.  <with-defaults> = 'report-all'

   The behavior of the <with-defaults> parameter handling for the value
   'report-all' is demonstrated in this example.

    <rpc message-id="101"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <get>
        <filter type="subtree">
          <interfaces xmlns="http://example.com/ns/interfaces"/>
        </filter>
        <with-defaults
         xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
          report-all
        </with-defaults>
      </get>
    </rpc>

    <rpc-reply message-id="101"
               xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <data>



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        <interfaces xmlns="http://example.com/ns/interfaces">
          <interface>
            <name>eth0</name>
            <mtu>8192</mtu>
            <status>up</status>
          </interface>
          <interface>
            <name>eth1</name>
            <mtu>1500</mtu>
            <status>up</status>
          </interface>
          <interface>
            <name>eth2</name>
            <mtu>9000</mtu>
            <status>not feeling so good</status>
          </interface>
          <interface>
            <name>eth3</name>
            <mtu>1500</mtu>
            <status>waking up</status>
          </interface>
        </interfaces>
      </data>
    </rpc-reply>

A.3.2.  <with-defaults> = 'report-all-tagged'

   The behavior of the <with-defaults> parameter handling for the value
   'report-all-tagged' is demonstrated in this example.  A 'tagged' data
   node is an element that contains the 'default' XML attribute, set to
   'true' or '1'.

   The actual data nodes tagged by the server depend on the default-
   handling basic mode used by the server.  Only the data nodes that are
   considered to be default data will be tagged.

   In this example, the server's basic mode is equal to 'trim', so all
   data nodes that would contain the schema default value are tagged.
   If the server's basic mode is 'explicit', then only data nodes that
   are not explicitly set data are tagged.  If the server's basic mode
   is 'report-all', then no data nodes are tagged.

    <rpc message-id="102"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <get>
        <filter type="subtree">
          <interfaces xmlns="http://example.com/ns/interfaces"/>
        </filter>



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        <with-defaults
         xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
          report-all-tagged
        </with-defaults>
      </get>
    </rpc>

    <rpc-reply message-id="102"
               xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
               xmlns:wd="urn:ietf:params:xml:ns:netconf:default:1.0">
      <data>
        <interfaces xmlns="http://example.com/ns/interfaces">
          <interface>
            <name>eth0</name>
            <mtu>8192</mtu>
            <status wd:default="true">up</status>
          </interface>
          <interface>
            <name>eth1</name>
            <mtu wd:default="true">1500</mtu>
            <status wd:default="true">up</status>
          </interface>
          <interface>
            <name>eth2</name>
            <mtu>9000</mtu>
            <status>not feeling so good</status>
          </interface>
          <interface>
            <name>eth3</name>
            <mtu wd:default="true">1500</mtu>
            <status>waking up</status>
          </interface>
        </interfaces>
      </data>
    </rpc-reply>

A.3.3.  <with-defaults> = 'trim'

   The behavior of the <with-defaults> parameter handling for the value
   'trim' is demonstrated in this example.

    <rpc message-id="103"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <get>
        <filter type="subtree">
          <interfaces xmlns="http://example.com/ns/interfaces"/>
        </filter>
        <with-defaults



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         xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
          trim
        </with-defaults>
      </get>
    </rpc>

    <rpc-reply message-id="103"
               xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <data>
        <interfaces xmlns="http://example.com/ns/interfaces">
          <interface>
            <name>eth0</name>
            <mtu>8192</mtu>
          </interface>
          <interface>
            <name>eth1</name>
          </interface>
          <interface>
            <name>eth2</name>
            <mtu>9000</mtu>
            <status>not feeling so good</status>
          </interface>
          <interface>
            <name>eth3</name>
            <status>waking up</status>
          </interface>
        </interfaces>
      </data>
    </rpc-reply>

A.3.4.  <with-defaults> = 'explicit'

   The behavior of the <with-defaults> parameter handling for the value
   'explicit' is demonstrated in this example.

    <rpc message-id="104"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <get>
        <filter type="subtree">
          <interfaces xmlns="http://example.com/ns/interfaces"/>
        </filter>
        <with-defaults
         xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-with-defaults">
          explicit
        </with-defaults>
      </get>
    </rpc>




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    <rpc-reply message-id="104"
               xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <data>
        <interfaces xmlns="http://example.com/ns/interfaces">
          <interface>
            <name>eth0</name>
            <mtu>8192</mtu>
            <status>up</status>
          </interface>
          <interface>
            <name>eth1</name>
            <status>up</status>
          </interface>
          <interface>
            <name>eth2</name>
            <mtu>9000</mtu>
            <status>not feeling so good</status>
          </interface>
          <interface>
            <name>eth3</name>
            <mtu>1500</mtu>
            <status>waking up</status>
          </interface>
        </interfaces>
      </data>
    </rpc-reply>

Authors' Addresses

   Andy Bierman
   Brocade

   EMail: andy.bierman@brocade.com


   Balazs Lengyel
   Ericsson
   Budapest,
   Hungary

   EMail: balazs.lengyel@ericsson.com










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