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Versions: 00 01 02

NETCONF Working Group                                           R. Varga
Internet-Draft                                 Pantheon Technologies SRO
Intended status: Standards Track                           March 3, 2014
Expires: September 02, 2014


            Efficient XML Interchange Capability for NETCONF
                 draft-varga-netconf-exi-capability-02

Abstract

   The Network Configuration Protocol (NETCONF) provides mechanisms to
   install, manipulate, and delete the configuration of network devices
   via exchange of XML messages in textual representation.  Efficient
   XML Interchange (EXI) is a W3C-recommended binary representation of
   XML Information Set, which is more efficient from both CPU and
   bandwidth utilization perspective.  This document defines a
   capability-based extension to the NETCONF protocol that allows peers
   to agree to exchange protocol messages using EXI encoding.

Requirements Language

   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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 02, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.






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   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.  EXI Capability . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Dependencies . . . . . . . . . . . . . . . . . . . . . . .  3
     3.3.  Capability Identifier  . . . . . . . . . . . . . . . . . .  3
     3.4.  Dynamic Schema-informed Encoding Negotiation . . . . . . .  4
     3.5.  New Mandatory Operations . . . . . . . . . . . . . . . . .  5
       3.5.1.  <start-exi>  . . . . . . . . . . . . . . . . . . . . .  5
       3.5.2.  <stop-exi> . . . . . . . . . . . . . . . . . . . . . .  8
     3.6.  New Optional Operations  . . . . . . . . . . . . . . . . .  8
       3.6.1.  <enable-schema-encoding> . . . . . . . . . . . . . . .  8
       3.6.2.  <disable-schema-encoding>  . . . . . . . . . . . . . .  9
   4.  YANG module for <start-exi> and <stop-exi> Operations  . . . .  9
   5.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 14
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   The NETCONF protocol [RFC6241] is defined in terms of two peers,
   client and server, exchanging XML messages in an RPC pattern.  These
   messages are encoded as XML text documents, which makes the exchange
   easily understandable by human operators by simply observing them on
   the wire.  Unfortunately, this feature takes its toll on both
   computation and network resources, as the representation contains
   redundant information and verbose names.

   Efficient XML Interchange [W3C.REC-exi-20110310] is a W3C
   Recommendation which defines a more efficient way of encoding XML
   Information Set than the usual text representation.  This is achieved
   by a combination of reduced verbosity, binary encoding and,
   optionally, pruning of non-essential information like comments.

   It seems advantageous to allow clients and servers participating on a
   NETCONF session to sacrifice human readability to increase processing
   efficiency, especially in environments with high transactional
   activity and/or limited computing resources.


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2.  Terminology

   This document uses the following terms defined in [RFC6241]:

   o  capability

   o  client

   o  message

   o  protocol operation

   o  remote procedure call

   o  server

3.  EXI Capability

3.1.  Overview

   The :exi capability indicates that the peer supports EXI message
   encoding and is willing to use it.  The capability has no effect on
   data being handled by the NETCONF protocol, nor does it affect
   protocol message exchanges.

3.2.  Dependencies

   EXI-encoded documents are binary data, this capability may only be
   used when the underlying transport is 8-bit clean and preserves
   message boundaries in face of arbitrary binary data.  Notably this
   requires use of Chunked Framing mechanism as described in [RFC6242]
   when used with SSH transport.

   The optional Dynamic Schema-informed Encoding Negotiation mechanism
   relies on NETCONF Monitoring as defined in [RFC6022].

3.3.  Capability Identifier

   The EXI capability is identified by the following capability string:

   urn:ietf:params:netconf:capability:exi:1.0

   The identifier MAY have a the following parameters:

   compression: This indicates that the sender is willing to perform EXI
      compression.  The parameter MUST contain a positive integral
      value, which indicates maximum compression block size which the
      sender can process.

   schemas: This indicates that the sender can use schema-informed
      grammars for EXI encoding.  The parameter MUST contain a value,
      which has to be one of "builtin", "base:1.1" or "dynamic".


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      builtin Indicates the ability to use the XML schema built into the
         EXI specification.

      base:1.1 Superset of "builtin", indicates that the sender
         additionally supports schema-informed EXI encoding, based on
         netconf.xsd schema published in [RFC6241].

      dynamic Superset of "base:1.1", indicates that the sender
         additionally supports dynamic schema-informed encoding
         negotiation outlined below.

   Examples:

      urn:ietf:params:netconf:capability:exi:1.0?compression=1000000

      urn:ietf:params:netconf:capability:exi:1.0?schemas=builtin

      urn:ietf:params:netconf:capability:exi:1.0?schemas=base:1.1

      urn:ietf:params:netconf:capability:exi:1.0?compression=20000&schem
      as=builtin

      urn:ietf:params:netconf:capability:exi:1.0?schemas=dynamic

3.4.  Dynamic Schema-informed Encoding Negotiation

   The core of this extension relies on shared knowledge between the
   server and the client where schema-informed encoding is concerned.
   This limits the encoding efficiency as the actual data transferred
   over the session is encoded using the equivalent of the builtin
   schema.  Alleviating this limitation requires a mechanism for
   discovering data schemas and a protocol for synchronizing their
   activation.

   The base schema discovery mechanism is already present in [RFC6022].
   This document extends the /netconf-state/schemas/schema subtree with
   a new leaf, exi-useable, which indicates whether the server supports
   the use of that particular schema in the EXI schema-informed encoding
   process.

   The negotiation of use of a particular schema for encoding has
   multiple aspects.  First and foremost is the concern of constrained
   environments, which may have limited resources and thus their ability
   to dedicate them to improving encoding efficiency may change over
   lifetime of a NETCONF session.  The second issue comes from the need
   to synchronize the values used in the "schema" EXI header field.
   Both end of the session need to map names to the same schemas,
   otherwise the decoding process will not succeed.  This name is
   carried verbatim in the stream, so it should be as concise as
   possible.




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   When the peers have both indicated support for Dynamic Schema-
   informed Encoding, encoding starts in base:1.1 mode.  The client then
   queries the server for the list of schemas, looking for schemas which
   have the exi-useable leaf set to true.  It then selects the schemas
   it can use in EXI encoding process, potentially requesting them from
   the server.  Finally it prioritizes them and sends a <enable-schema-
   encoding> request for each of them.  Once the server has assigned a
   EXI schema-id and communicated it back the the client, both parties
   can use this schema in EXI encoding.  The client can request the end
   of use of a particular schema via the <disable-schema-encoding> RPC,
   which the server SHOULD NOT fail.

3.5.  New Mandatory Operations

3.5.1.  <start-exi>

   Description: The <start-exi> operation requests that the message
      encoding be switched to EXI.  The operation is invoked by the
      client and validated by the server.  If the server finds the
      parameters acceptable, it will issue a positive response in the
      current session encoding.  It MUST encode all subsequent messages
      using EXI encoding with the supplied parameters.  It will also
      expect all incoming messages to be EXI-encoded.  The client MUST
      NOT send any messages to the server between the time is sends this
      request and the time it receives a response.  Once it receives a
      positive reply, it MUST encode all subsequent messages using the
      EXI encoding with the parameters supplied in the RPC.  If the
      operation fails, the session message encoding remains unchanged.

   Parameters:

      alignment: Requested EXI alignment.  If this parameter is not
         present, bit-packed is assumed.  The following values are
         valid:

         bit-packed: Set EXI alignment to bit-packed.

         byte-aligned: Set EXI alignment to byte-aligned.

         pre-compression: Set EXI alignment to pre-compression.

         compressed: Do not specify EXI alignment, but perform EXI
            compression instead.

      fidelity: Requested EXI fidelity options.  If this parameter is
         not present or empty, all fidelity options are disabled.  The








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         following items may be specified:

         <comments/>: Preserve.comments EXI Fidelity option

         <dtd/>: Preserve.dtd EXI Fidelity option

         <lexical-values/>: Preserve.lexicalValues EXI Fidelity option

         <pis/>: Preserve.pis EXI Fidelity option

         <prefixes/>: Preserve.prefixes EXI Fidelity option

      schema: Optional parameter.  This specifies what schema options
         should be enabled in the EXI encoding process.  The following
         values are valid:

         none Do not use schema-informed grammars at all.  This
            translates to using schemaId of <xsd:nil>true</xsd:nil> in
            the EXI Options header.

         builtin Do no use schema-informed grammars, but use the built-
            in XML data types.  This translates to using an empty
            schemaId in the EXI Options header.

         base:1.1 Use schema-informed grammar based on netconf.xsd as
            published in [RFC6241] in non-strict mode.  The value
            "base:1.1" should be carried in the schemaId field in the
            EXI Options.

         dynamic Same as base:1.1 with the additional support for
            dynamically modifying which schemas are available for
            schema-informed encoding.

   Positive Response: If the device was able to satisfy the request, an
      <rpc-reply> is sent that contains an <ok> element.

   Negative Response: An <rpc-error> element is included in the <rpc-
      reply> if the request cannot be completed for any reason.

   Example:















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       <rpc message-id="101"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
           <start-exi>
               <alignment>pre-compression</alignment>
               <fidelity>
                   <dtd/>
                   <lexical-values/>
               </fidelity>
           </start-exi>













































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       </rpc>

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

3.5.2.  <stop-exi>

   Description: The <stop-exi> operation requests that the message
      encoding be switched to textual XML.  The operation is invoked by
      the client and validated by the server.  If the server is able to
      switch the encoding to XML, it will issue a positive response in
      the current session encoding.  It MUST encode all subsequent
      messages using standard XML encoding.  It will also expect all
      incoming messages to be XML-encoded.  The client MUST NOT send any
      messages to the server between the time is sends this request and
      the time it receives a response.  Once it receives a positive
      reply, it MUST encode all subsequent messages using the standard
      XML encoding.  If the operation fails, the session message
      encoding remains unchanged.  If the session currently uses XML
      encoding, this RPC is a no-operation and SHOULD NOT fail.

   Positive Response: If the device was able to satisfy the request, an
      <rpc-reply> is sent that contains an <ok> element.

   Negative Response: An <rpc-error> element is included in the <rpc-
      reply> if the request cannot be completed for any reason.

   Example:

       <rpc message-id="101"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
           <stop-exi/>
       </rpc>

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

3.6.  New Optional Operations

3.6.1.  <enable-schema-encoding>

   Description: The <enable-schema-encoding> requests the device assign
      a numeric identifier for use of a specific schema for EXI Schema-
      informed encoding.

   Parameters:

      identifier: Schema identifier, as defined in [RFC6022].

      version: Schema version, as defined in [RFC6022].

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      format: Schema format, as defined in [RFC6022].

   Positive Response: If the device was able to satisfy the request, an
      <rpc-reply> is sent that contains an <exi-schema-id> element,
      which contains the numeric identifier which should be used in the
      schemaId EXI header field.  This identifier has to be unique.

   Negative Response: An <rpc-error> element is included in the <rpc-
      reply> if the request cannot be completed for any reason.

3.6.2.  <disable-schema-encoding>

   Description: The <disable-schema-encoding> requests the device to
      deallocate the schema ID from use on this session and stop using
      it for encoding data towards the client.

   Parameters:

      exi-schema-id: EXI Schema ID, as assigned by a previous <enable-
         schema-encoding> call.

   Positive Response: If the device was able to satisfy the request, an
      <rpc-reply> is sent that contains an <ok> element.

   Negative Response: An <rpc-error> element is included in the <rpc-
      reply> if the request cannot be completed for any reason.

4.  YANG module for <start-exi> and <stop-exi> Operations

   The following YANG module defines the new operations introduced in
   this document.  The YANG language is defined in [RFC6020].  Every
   NETCONF speaker that supports the :exi capability MUST implement this
   YANG module.





















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   <CODE BEGINS> file "ietf-netconf-exi@2014-03-03.yang"

   module ietf-netconf-exi {
       // vi: set et smarttab sw=4 tabstop=4:
       namespace "urn:ietf:params:xml:ns:netconf:exi:1.0";

       prefix exi;

       import ietf-netconf-monitoring {
           prefix ncm;
           revision-date "2010-10-04";
       }

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

       contact
           "Robert Varga <robert.varga@pantheon.sk>";

       description
           "NETCONF Protocol Operations for Efficient XML Interchange.";

       revision 2014-03-03 {
           description
               "Updated with dynamic schema negotiation.";
           reference
               "I-D.varga-netconf-exi-capability-02";
       }

       revision 2013-10-21 {
           description
               "Initial revision";
           reference
               "I-D.varga-netconf-exi-capability-01";
       }

       typedef exi-alignment {
           type enumeration {
               enum bit-packed {
                   description
                       "Use bit-packed EXI alignment";
               }
               enum byte-aligned {
                   description
                       "Use byte-aligned EXI alignment";
               }
               enum pre-compression {
                   description
                       "Use pre-compression EXI alignment";
               }
               enum compressed {
                   description

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                       "Do not set EXI alignment, use EXI compression
                       instead";
               }
           }

           description "EXI alignment specification.";
       }

       typedef exi-fidelity {
           type enumeration {
               enum comments {
                   description
                       "Preserve.comments EXI Fidelity option";
               }
               enum dtd {
                   description
                       "Preserve.dtd EXI Fidelity option";
               }
               enum lexical-values {
                   description
                       "Preserve.lexicalValues EXI Fidelity option";
               }
               enum pis {
                   description
                       "Preserve.pis EXI Fidelity option";
               }
               enum prefixes {
                   description
                       "Preserve.prefixes EXI Fidelity option";
               }
           }

           description "EXI fidelity options.";
       }

       rpc start-exi {
           description
               "Start encoding protocol messages in Efficient XML
               Interchange format.";

           reference "I-D.varga-netconf-exi-capability";

           input {
               leaf alignment {
                   type exi-alignment;
                   default "bit-packed";
                   description "EXI alignment to use.";
               }

               leaf-list fidelity {
                   type exi-fidelity;
                   description "EXI fidelity options to use.";
               }
           }

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       }

       rpc stop-exi {
           description
               "Stop encoding protocol messages in Efficient XML
               Interchange format. Revert back to using the usual text
               XML encoding.";
       }

       grouping schema-identifier {
           description
               "The globally-unique identifier of a schema. This
               grouping contains the verbatim transcription of arguments
               to <get-schema> RPC as defined in RFC6022, except all
               leaves are made mandatory.";

           leaf identifier {
               type string;
               mandatory true;
               description
                   "Identifier for the schema list entry.";
           }

           leaf version {
               type string;
               description
                   "Version of the schema requested.  If this parameter
                   is not present, and more than one version of the
                   schema exists on the server, a 'data-not-unique'
                   error is returned, as described above.";
           }

           leaf format {
               type identityref {
                   base ncm:schema-format;
               }
               description
                   "The data modeling language of the schema.  If this
                   parameter is not present, and more than one formats
                   of the schema exists on the server, a
                   'data-not-unique' error is returned, as described
                   above.";
           }
       }

       typedef exi-schema-id {
           type uint16;
           description
               "Schema identifier for use in the EXI stream header.";
       }

       augment "/ncm:netconf-state/ncm:schemas/ncm:schema" {
           description
               "Additional information about schemas useful for EXI

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               encoding";

           leaf exi-useable {
               type boolean;
               default false;
               description
                   "Set to true if the device can use the schema for EXI
                   Schema-informed encoding.";
           }
           leaf exi-schema-id {
               type exi-schema-id;
               description
                   "The EXI schema ID currently assigned to this schema.
                   This value has meaning only within the session and
                   may differ on other sessions.";
           }
       }

       rpc enable-schema-encoding {
           description
               "Request the use of specificied schema in EXI message
               encoding.  This request is sent by the client to the
               server. If the server is able to transition into using
               the schema, it assigns it a unique EXI integer
               identifier.  This identifier is to be used in the EXI
               header as schema identifier.

               The server may start using the identifier as soon as it
               enqueus the response. The client may start using the
               identifier as soon as it sees this RPC complete.";
           input {
               uses schema-identifier;
           }
           output {
               leaf exi-schema-id {
                   type exi-schema-id;
                   mandatory true;
                   description
                       "The EXI Schema ID assigned to this schema for
                       encoding purposes.";
               }
           }
       }

       rpc disable-schema-encoding {
           description
               "This RPC is send by the client when it stops using a
               particular exi-schema-id.";
           input {
               leaf exi-schema-id {
                   type exi-schema-id;
                   mandatory true;
                   description
                       "The EXI Schema ID which should be disabled.";

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               }
           }
       }
   }


5.  IANA considerations

   This document registers the following capability identifier URN in
   the 'Network Configuration Protocol (NETCONF) Capability URNs'
   registry: urn:ietf:params:netconf:capability:exi:1.0

6.  Security Considerations

   The compression option present in EXI specification may increase CPU
   and memory requirements for encoding the response.  Devices should
   ensure this overhead is acceptable before agreeing to using EXI
   encoding, such that no operational risks are introduced.

7.  Acknowledgements

   The author would like to thank Anton Tkacik, Miroslav Miklus and
   Stefan Kobza for their contributions to this document.

8.  Normative References

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

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

   [RFC6022]  Scott, M. and M. Bjorklund, "YANG Module for NETCONF
              Monitoring", RFC 6022, October 2010.

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

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [W3C.REC-exi-20110310]
              Schneider, J. and T. Kamiya, "Efficient XML Interchange
              (EXI) Format 1.0", World Wide Web Consortium
              Recommendation REC-exi-20110310, March 2011, <http://
              www.w3.org/TR/2011/REC-exi-20110310>.

Author's Address





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   Robert Varga
   Pantheon Technologies SRO
   Mlynske Nivy 56
   Bratislava  821 05
   Slovakia

   Email: robert.varga@pantheon.sk














































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