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Versions: (draft-bierman-netconf-with-defaults) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6243

NETCONF                                                       A. Bierman
Internet-Draft                                           Netconf Central
Intended status: Standards Track                              B. Lengyel
Expires: August 21, 2009                                        Ericsson
                                                       February 17, 2009


                  With-defaults capability for NETCONF
                  draft-ietf-netconf-with-defaults-00

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   document authors.  All rights reserved.

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Abstract

   The NETCONF protocol defines ways to read configuration data from a



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   NETCONF agent.  Part of this data is not set by the NETCONF manager,
   but rather a default value is used.  In many situations the NETCONF
   manager has a priori knowledge about default data, so the NETCONF
   agent does not need to send it to the manager.  In other situations
   the NETCONF manger will need this data as part of the NETCONF <rpc-
   reply> messages.  This document defines a capability-based extension
   to the NETCONF protocol that allows the NETCONF manager to control
   whether default values are part of NETCONF <rpc-reply> messages.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.1.  Requirements Notation  . . . . . . . . . . . . . . . .  3
       1.1.2.  NETCONF Terms  . . . . . . . . . . . . . . . . . . . .  3
   2.  With-defaults Capability . . . . . . . . . . . . . . . . . . .  4
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
       2.1.1.  Basic handling of default data . . . . . . . . . . . .  4
     2.2.  Dependencies . . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Capability Identifier  . . . . . . . . . . . . . . . . . .  5
     2.4.  New Operations . . . . . . . . . . . . . . . . . . . . . .  5
     2.5.  Modifications to Existing Operations . . . . . . . . . . .  5
   3.  Interactions with Other Capabilities . . . . . . . . . . . . .  7
   4.  Data Model XSD . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Other default handling methods in the real world?  . . . . 10
     7.2.  XSD needed?  . . . . . . . . . . . . . . . . . . . . . . . 10
     7.3.  Use the NETCONF namespace? . . . . . . . . . . . . . . . . 10
   8.  Appendix A  -  Change Log  . . . . . . . . . . . . . . . . . . 11
     8.1.  -00  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14















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1.  Introduction

   The NETCONF protocol defines ways to read configuration data from a
   NETCONF agent.  Part of this data is not set by the NETCONF manager,
   but rather a default value is used.  In many situations the NETCONF
   manager has a priori knowledge about default data, so the NETCONF
   agent does not need to send it to the manager.  A priori knowledge
   can be e.g. a document formally describing the data models supported
   by the NETCONF agent.

   A networking device may have a large number of default values.  Often
   the default values are not interesting or specifically defined with a
   "reasonable" value, so that the management user does not have 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 manager will need the
   default data from the node:

   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 theses cases the NETCONF manager will need default data as
   part of the NETCONF <rpc-reply> messages.

   This document defines a capability-based extension to the NETCONF
   protocol that allows the NETCONF manager to control whether default
   data is part of NETCONF <rpc-reply> messages.

1.1.  Terminology

1.1.1.  Requirements Notation

   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].

1.1.2.  NETCONF Terms

   o  Default data: Data that is set or used by the NETCONF agent
      whenever the NETCONF manager does not provide a specific value for
      the relevant data item.  Default values are often specified in
      documents describing the data models supported by the NETCONF



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      agent.  In the context of this document only configuration data is
      considered, state data is excluded.

   o  Explicitly set default data: Data that is explicitly set by the
      NETCONF manager to it's default value.  Some agents MIGHT treat
      explicitly set default data as simple default data, as they MIGHT
      not be able to differentiate between them.

   In addition the following terms are defined in RFC 4741 and are not
   redefined here:
   o  agent
   o  application
   o  manager
   o  operation
   o  RPC
   o  RPC request
   o  RPC response


2.  With-defaults Capability

2.1.  Overview

   The :with-defaults capability indicates that the NETCONF agent makes
   it possible for the NETCONF manager to control whether default data
   is part of NETCONF <rpc-reply> messages.  The capability only affects
   configuration data not state data.  Sending of default data is
   controlled for each individual operation separately.  The NETCONF
   agent MUST also indicate its basic behavior, whether it sends default
   data in the absence of any specific request from the NETCONF manager.

2.1.1.  Basic handling of default data

   It is not defined in [RFC4741], whether default data is part of the
   datastore/data model, or if it is meta data, that influences the
   behavior of the NETCONF server, device but is not actually part of
   the datastore.  This document intentionally avoids deciding this
   question.

   As a consequence of this issue, NETCONF servers that do not implement
   the :with-defaults capability may or may not return default data in
   NETCONF <rpc-reply> messages.

   Different NETCONF agents report default data in different ways.  This
   document specifies the following three basic methods:






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   o  Report all: All default data is always reported.
   o  Trim: Values are not reported if they match the default.
   o  Explicit: Report values if they are explicitly set.

2.2.  Dependencies

   None

2.3.  Capability Identifier

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

   The identifier MUST have an additional parameter: "basic".  This
   indicates how the agent reports default data in <rpc-reply> messages,
   in the case the manager does not specify the required behavior in the
   <rpc> request.  The allowed values of this parameter are report-all,
   trim, explicit as defined in Section 2.1.1.  E.g.:

   urn:ietf:params:netconf:capability:with-defaults?basic=report-all

2.4.  New Operations

   None

2.5.  Modifications to Existing Operations

   A new <with-defaults> XML element is added to the 'method-name'
   element.  This is the element that indicates the type of the
   operation e.g. <get>, <get-config> or <copy-config>.  If the <with-
   defaults> element is present, it controls the reporting of default
   data.  The agent MUST return default data in the NETCONF <rpc-reply>
   messages according to the value of the element.

   Allowed values of the with-defaults element are:

   o  false: default data SHOULD NOT be returned.
   o  true: all default data MUST be returned.

   If the <with-defaults> element is not present, the agent follows its
   basic behavior as indicated by the capability identifier's parameter
   see Section 2.3.

   The 'with-defaults' element is defined in the namespace specified as
   the 'targetNamespace' in Section 4.  However, an agent MUST accept it
   even if no namespace is used.

   Affected operations:




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   o  <get>
   o  <get-config>
   o  <copy-config>

   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.

   The following example shows a <get> operation which is using the
   'with-defaults' element.  The manager is retrieving the 'interfaces'
   object, defined in the example.com data model.  (In this simple
   example, the 'name' field is defined as the key, and the 'mtu' field
   is the only other data in the <interface> element).  The default
   value of mtu is '1500'.  The basic default handling for the agent is
   "trim".  As the 'with-defaults' element has the value 'true', the mtu
   is returned not just for eth0 but also for eth1.



       <rpc message-id="102"
            xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
         <get>
           <with-defaults>true</with-defaults>
           <filter type="subtree">
             <interfaces xmlns="http://example.com/interfaces/1.2"/>
           </filter>
         </get>
       </rpc>

       <rpc-reply message-id="102" with-defaults="true"
            xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
         <data>
           <interfaces xmlns="http://example.com/interfaces/1.2">
             <interface>
               <name>eth0</name>
               <mtu>8192</mtu>
             </interface>
             <interface>
               <name>eth1</name>
               <mtu>1500</mtu>
             </interface>
           </interfaces>
         </data>
       </rpc-reply>




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                                 Figure 1


3.  Interactions with Other Capabilities

   None


4.  Data Model XSD

   This section contains an XML Schema Definition
   [W3C.REC-xmlschema-2-20041028] which defines the XML syntax
   associated for the with-defaults XML element.



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

     <xs:annotation>
       <xs:documentation>
         Schema defining the with-defaults element.

         Organization: "IETF NETCONF Working Group"
         Contact Info: balazs.lengyel@ericsson.com
       </xs:documentation>
     </xs:annotation>

     <xs:element name="with-defaults"
       type="xs:boolean"/>

   </xs:schema>



5.  IANA Considerations

   This document registers two URIs for the NETCONF XML namespace in the
   IETF XML registry [RFC3688].  Note that the capability URN is
   compliant to [RFC4741] section 10.3.







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   +---------------+---------------------------------------------------+
   | Index         | Capability Identifier                             |
   +---------------+---------------------------------------------------+
   | :with-default | urn:ietf:params:netconf:capability:with-defaults: |
   | s             | 1.0                                               |
   +---------------+---------------------------------------------------+

   URI: urn:ietf:params:xml:ns:netconf:with-defaults:1.0

   Registrant Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.







































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6.  Security Considerations

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

   The 'with-defaults' capability provides manager controls over the
   retrieval of particular types of XML data from a configuration
   database.  They only suppress data that can already be retrieved with
   the standard protocol operations, and do not add any data to the
   configuration database.








































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7.  Open Issues

7.1.  Other default handling methods in the real world?

   Are there any other basic default handling methods out there we need
   to include?

7.2.  XSD needed?

   Is the XSD needed?  Does it add any value, any clarity to the
   document?

7.3.  Use the NETCONF namespace?

   Would it be possible to put the with-defaults element into the
   NETCONF namespace?  Is the current statement: "However, an agent MUST
   accept it even if no namespace is used." acceptable?


































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8.  Appendix A  -  Change Log

8.1.  -00

   Created from draft-bierman-netconf-with-defaults-01.txt

   It was decided by the NETCONF mailing list, that with-defaults should
   be a sub-element of each affected operation.  While this violates the
   XSD of RFC4741 this is acceptable and follows the ideas behind
   NETCONF and YANG.

   Hopefully it will be clarified in the 4741bis RFC whether such
   extensions are allowed.






































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9.  Acknowledgements

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














































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10.  Normative References

   [W3C.REC-xmlschema-2-20041028]
              Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium
              Recommendation REC-xmlschema-2-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.

   [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.



































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Authors' Addresses

   Andy Bierman
   Netconf Central
   Simi Valley, CA
   USA

   Email: andy@netconfcentral.com


   Balazs Lengyel
   Ericsson
   Budapest,
   Hungary

   Email: balazs.lengyel@ericsson.com



































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