netconf                                                           B. Liu
Internet-Draft                                                  G. Zheng
Intended status: Standards Track                     Huawei Technologies
Expires: April 30, 2015                                 October 27, 2014


               A NETCONF Extension for Data Fragmentation
                   draft-liu-netconf-fragmentation-01

Abstract

   This document introduces an extension to NETCONF (Network
   Configuration) protocol.  The extension allows NETCONF to handle
   large size data as fragmented RPC messages.  Specifically, this
   document defines a new <get-block> capability and relevant operations
   to handle the fragmentations.

Status of This Memo

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

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   This Internet-Draft will expire on April 30, 2015.

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language and Terminology . . . . . . . . . . . .   3
   3.  Current Large size Handling Methods and Problems  . . . . . .   3
     3.1.  Stream-Oriented Handling  . . . . . . . . . . . . . . . .   3
     3.2.  Requesting a Portion of Data  . . . . . . . . . . . . . .   4
   4.  Candidate Solutions . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Netconf Fragmentation Mechanism . . . . . . . . . . . . .   4
       4.1.1.  Fragmentation Requirements  . . . . . . . . . . . . .   4
       4.1.2.  <get-block> extention . . . . . . . . . . . . . . . .   5
     4.2.  Subtree Iteration . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Linked Replies  . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Examples of the Candidate Solutions  . . . . . . . .   8
     A.1.  <get-next> (RPC Fragmentation) Example  . . . . . . . . .   8
     A.2.  <get-list> (Subtree Iteration) Example  . . . . . . . . .  10
     A.3.  Linked-replies Example  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   NETCONF [RFC6241] is the next generation network management protocol
   for configuring devices.  It is becoming more and more popular, and
   some NMS (Network Management System) only use NETCONF as its
   southbound interface.  The message procedures of NETCONF are based on
   RPC (Remote Procedure Call) interactions.  A NETCONF client/server
   sends a <rpc> message to the counterpart and then receives a replying
   <rpc-reply> message.

   In some situations, the <rpc-reply> message might be very large.  For
   example, when NMS is retrieving a large amount of routes in a core
   router or doing a full-synchronizing with a device, the <rpc-reply>
   data might exceed Mega-Byte amount.  Then there comes the problem of
   how to handle the large size data.  In Section 3, this document
   briefly introduces two typical ways of current handling on this
   issue; and analyzes the problems of them.

   To fix the problems, in Section 4, this document proposes a method of
   extending the NETCONF protocol to allow handling large size data as
   fragmented <rpc-reply> messages.  The fragmentation is done at the
   NETCONF level, so it allows the NETCONF client to terminate the large
   size data processing momentarily by protocol interactions; and also



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   allows the fragmented messages to be instantly parsed piece by piece.
   Specifically, the fragmentation is achieved through a newly defined
   <get-block> capability and relevant operations.

2.  Requirements Language and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

   Terminology:

   DOM: Document Object Model, which is a cross-platform and language-
   independent convention for representing and interacting with objects
   in HTML, XHTML and XML documents.  Objects in the DOM tree may be
   addressed and manipulated by using methods on the objects.  [DOM]

   SAX: Simple API for XML, which is an event sequential access parser
   API developed by the XML-DEV mailing list for XML documents.  SAX
   provides a mechanism for reading data from an XML document that is an
   alternative to that provided by the DOM.  Where the DOM operates on
   the document as a whole, SAX parsers operate on each piece of the XML
   document sequentially.  [SAX]

   libxml: a software library for parsing XML documents.  [LIBXML]

   <get-block>: a capability and operation defined in this document to
   handle large size

3.  Current Large size Handling Methods and Problems

3.1.  Stream-Oriented Handling

   Stream-Oriented handling mainly includes the following two aspects:

   o  The server encapsulates the large size replying data in a <rpc-
      reply> message and streams it to the client through TCP protocol.

   o  The client parses the received <rpc-reply> content in a stream-
      oriented way.  More specifically, the client could utilize SAX
      [SAX-PARSING] to instantly parse the received content without
      waiting for the whole message been transported.

   Problems:



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   o  Stream-Oriented method lacks the capability of discontinuing large
      size processing in the server.  It would cause unnecessary
      resource/performance cost in the devices if the NMS has already
      got the intended portion or just canceled by the administrators.

   o  Another problem is the implementation of SAX parsing is more
      complex than DOM parsing [DOM-PARSING] in the Netconf client.
      More computing burden will be taken in Netconf client to support
      SAX parsing.

3.2.  Requesting a Portion of Data

   The clients actively limit the search range of the data so that the
   servers only need to reply with a part of the large size data.  Thus
   the clients could control the replies in a reasonable size.  One
   example is that the clients get a list of the content, and provide a
   start offset and a max-count, to get a portion at a time.

   Problems:

   o  This method has an implication that the client needs to know the
      list/index of the intended large size data in advance before it
      starting the search request.  It can't fit the scenarios of real-
      time on-demand data retrieving.  And there is no standard to
      specify the list/index format in a uniform way.  Thus it is only
      suitable for private implementation, thus multi-vendor interaction
      is not supported.

   o  More important, it is just an indirect way to solve the problem.
      It could not fit the scenarios where the client just needs the
      whole large size data in the server.

4.  Candidate Solutions

   (Editor notes: this section discusses several possible solutions.
   The fragmentation mechanism is the original proposal of the draft.
   The other two were proposed during mailing list discussion by Andy
   Bierman and Juergen Schoenwaelder respectively.  We include all of
   them for discussion and solution selection.)

4.1.  Netconf Fragmentation Mechanism

4.1.1.  Fragmentation Requirements

   this document proposes an RPC fragmentation mechanism to handle the
   large size data.  Two essential requirements of the fragmentation
   are:




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   o  It needs to allow the NETCONF client to terminate the large size
      data processing momentarily by protocol interactions.  In the
      proposed mechanisms in this draft, when the NETCONF server replies
      the client an <rpc-reply> fragmentation, it will wait the response
      from the client that whether it needs to send the next
      fragmentation.  So if the initiator has got the intended portion,
      it could terminate the large size process immediately.

   o  It needs to allow the NETCONF client to instantly parse the
      fragmentations piece by piece through the more widely supported
      DOM parsing.  So in this document, it specifies that each <rpc-
      reply> fragmentation MUST be in a complete XML form.

4.1.2.  <get-block> extention

   o Function

      The devices can only use <get-block> operation when the Get-block
      capability was announced.

      The <get-block> fragmentation rules are:

      A.  There should be a Max-Size for fragmentation.  [Open
          Question]Should there be a clear specification of the size?
          E.g. 64K bytes.

      B.  When the message reaches the Max-Size, it is sent to the
          client and the next message could be created in advance.

      C.  Different records from one same table could be put into
          different <rpc-reply> messages

      D.  All of the fields in one record MUST be put into one <rpc-
          reply> message.

      E.  XML syntax MUST be complete in each fragmented message, so
          that each fragmentation could be parsed individually.

      F.  If the record(s) of the child node(s)/table(s) and the parent
          node(s)/table(s) are replied in different fragmentations, the
          child node/table fragmentations MUST include the path and
          index information of all the ancestor node(s)/table(s) in a
          hierarchical mode.

   o Parameters






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      <discard/>: in <get-block> operation&#65292; if the <discard/>
      parameter is conveyed, it means the operation is terminated.  Then
      it doesn't need to reply the remaining fragmentations.

   o Successful Operation Reply

      A <rpc-reply> message conveying a <data> element indicates the
      operation is successful.

      If there exists a next fragment, then an set-id attribute MUST be
      included in the <rpc-reply> messge.  The attribute set-id is used
      to identify different fragment sets.

   o Exception Handling

      After the NETCONF server replies a fragment, if there is no
      corresponding Get-block request from the client in a reasonable
      period (the time valued to be specified in the future), then the
      server release the offset of the replying data and cannot use
      <get-block> operation anymore, and the remaining data needs to be
      replied.

   Please refer to Appendix A.1 for an example.

4.2.  Subtree Iteration

   An "iterator" approach allows a list resource to be retrieved in
   chunks.  An RPC function could be added to do the iteration
   operation.

   Please refer to Appendix A.2 for an example.

   There is a problem with rapidly changing lists (could get repeat
   entries on miss some entries).

4.3.  Linked Replies

   Another solution is to change or augment NETCONF at some point in
   time such that an <rpc> can lead to a sequence of <rpc-reply> with a
   suitable cancel mechanism.  A simple approach is to add a linked-
   replies capability.  If a server announces "linked-replies"
   capablility and the client supports it as well, the client can add an
   additional parameter to an rpc to indicate the possible use of
   linked-replies.

   Please refer to Appendix A.3 for an example.





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   This would address the concern of large data retrievals but would
   also allow long running asynchronous rpcs (the ping or traceroute
   example).  This approach may lead to better support for asynchronous
   rpcs and rpcs that potentially return very large chunks of data than
   trying to solve this problem without enhancements of the rpc layer.
   Design details concerning data merging, error handling, how to send a
   cancel for a given link-id (e.g., by sending a new <rpc-cancel>
   message with a matching link-id) and whether it is necessary to
   negotiate linked rpc-reply sizes or whether it is good enough for the
   server to decide freely as it likes etc. need further study.

5.  Security Considerations

   TBD.

6.  IANA Considerations

   This draft does not request any IANA action.

7.  Acknowledgements

   Gang Yan and Shouchuan Yang made significant contribution to form the
   draft.  Valuable comments were received from Andy Bierman, Martin
   Bjorklund, Juergen Schoenwaelder, Chong Feng and some other people in
   Netconf working group.

   This document was produced using the xml2rfc tool [RFC2629].
   (initiallly prepared using 2-Word-v2.0.template.dot.  )

8.  References

8.1.  Normative References

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

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

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

8.2.  Informative References

   [DOM]      "http://en.wikipedia.org/wiki/Document_Object_Model", .





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   [DOM-PARSING]
              "http://www.w3.org/TR/DOM-Parsing/", .

   [LIBXML]   "http://xmlsoft.org/", .

   [SAX]      "http://en.wikipedia.org/wiki/Simple_API_for_XML", .

   [SAX-PARSING]
              "http://www.saxproject.org/apidoc/org/xml/sax/
              Parser.html", .

Appendix A.  Examples of the Candidate Solutions

A.1.  <get-next> (RPC Fragmentation) Example

Example 1: Get the next fragment
     <rpc message-id="101"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0">
       <get-config>
         <source>
           <running/>
         </source>
         <filter type="subtree">
           <top xmlns="http://example.com/schema/1.2/config">
             <users/>
           </top>
         </filter>
       </get-config>
     </rpc>

     <rpc-reply message-id="101"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0"
          xmlns:hw=http://www.huawei.com/NETCONF/capability/base/1.0
hw:set-id="101">
       <data>
         <top xmlns="http://example.com/schema/1.2/config">
           <users>
             <user>
               <name>root</name>
               <type>superuser</type>
               <full-name>Charlie Root</full-name>
               <company-info>
                 <dept>1</dept>
                 <id>1</id>
               </company-info>
             </user>
             <!-- additional <user> elements appear here... -->
           </users>



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         </top>
       </data>
     </rpc-reply>

<rpc message-id="102"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0">
       <get-block xmlns="http://www.huawei.com/NETCONF/capability/base/1.0"
set-id="1">
       </get-block>
     </rpc>
     <rpc-reply message-id="102"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0"
          xmlns:hw=http://www.huawei.com/NETCONF/capability/base/1.0
hw:set-id="101">
       <data>
         <top xmlns="http://example.com/schema/1.2/config">
           <users>
             <user>
               <name>admin</name>
               <type>commonuser</type>
               <full-name>Jim Green</full-name>
               <company-info>
                 <dept>9</dept>
                 <id>90</id>
               </company-info>
             </user>
             <!-- additional <user> elements appear here... -->
           </users>
         </top>
       </data>
     </rpc-reply>

Example 2: Abandon the remaining fragments
     <rpc message-id="103"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0">
       <get-block xmlns=http://www.huawei.com/NETCONF/capability/base/1.0 set-id="1">
         <discard/>
       </get-block>
     </rpc>

     <rpc-reply message-id="103"
          xmlns="urn:ietf:params:xml:ns:NETCONF:base:1.0">
       <ok/>
     </rpc-reply>

Example 3: Following is an example of the rule f in Section 4.1.2.
The child eTable is in a different message with the parents
aTable->bTable->cTable->dTable. Then the path and index information



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of all the ancestors MUST included in the search data.

<aTable>
  <aEntity>
  <aIndex1>
  </aEntity>
  <bTable>
    <bEntity>
<bIndex1>
</bEntity>
<eTable>
  <eEntity>
    <eIndex1>
    <ef2>
    <ef3>
  </eEntity>
</dTable>
  </bTable>
</aTable>


A.2.  <get-list> (Subtree Iteration) Example

   rpc get-list {
     input {
       leaf target {
          type schema-instance-identifier;
          description "Identifies subtree to retrieve.";
      }
      leaf start {
         type uint32;
         default 0;
         description "Number of entries to skip before starting retrieval";
      }
      leaf max-entries {
        type uint32 { range "1..max"; }
        default 25;
        description "Maximum number of list entries to retrieve";
      }
    }
    output {
       anyxml data {
          description "Contains the requested data";
       }
    }
  }

  <rpc>



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    <get-list>
      <target>/if:interfaces/if:interface</target>
    </get-list>
  </rpc>


  <rpc-reply>
     <data>
        <interfaces>
           <interface>   .... first entry </interface>
           ...
           <interface>   .... 25th entry </interface>
        </interfaces>
     </data>
  </rpc-reply>


   <rpc>
    <get-list>
      <target>/if:interfaces/if:interface</target>
      <start>25</start>
    </get-list>
  </rpc>


  <rpc-reply>
     <data>
        <interfaces>
           <interface>   .... 26th entry </interface>
           ...
           <interface>   .... 50th entry </interface>
        </interfaces>
     </data>
  </rpc-reply>


A.3.  Linked-replies Example














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Here is what a new client might do if it wants to use linked replies:

  <rpc message-id="101" link-id="123" xmlns="...">
  </rpc>

  The server can either simply send an rpc-reply or it starts sending
  linked replies, e.g.:

  <rpc-reply message-id="101" next-message-id="102" link-id="123" xmlns="...">
  </rpc-reply>

  <rpc-reply message-id="102" next-message-id="103" link-id="123" xmlns="...">
  </rpc-reply>

  <rpc-reply message-id="103" link-id="123" xmlns="...">
  </rpc-reply>

Authors' Addresses

   Bing Liu
   Huawei Technologies
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: leo.liubing@huawei.com


   Guangying Zheng
   Huawei Technologies
   Huawei Nanjing R&D Center
   101 Software Avenue, Yuhua District, Nanjing, Jiangsu, 210012
   P.R. China

   Email: zhengguangying@huawei.com
















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