A NETCONF Extension for Data Fragmentation
draft-liu-netconf-fragmentation-00
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draft-liu-netconf-fragmentation-00
Network Working Group B. Liu
Internet Draft G. Zheng
Intended status: Informational Huawei Technologies
Expires: December 6, 2014 June 4, 2014
A NETCONF Extension for Data Fragmentation
draft-liu-netconf-fragmentation-00.txt
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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.
Table of Contents
1. Introduction ................................................. 3
2. Requirements Language and Terminology ........................ 3
3. Problem Statement ............................................ 4
3.1. Current Large size Handling Methods ..................... 4
3.1.1. Stream-Oriented Handling ........................... 4
3.1.2. Requesting a Portion of Data ....................... 4
3.2. Problems ................................................ 4
4. Solution ..................................................... 5
4.1. Rationale: Standardized RPC Fragmentation Handling ...... 5
4.2. Design Choice: <get-block> extension .................... 5
4.2.1. <get-block> Capability ............................. 6
4.2.2. <get-block> Operation .............................. 6
4.2.3. Examples ........................................... 8
5. Security Considerations ..................................... 11
6. IANA Considerations ......................................... 11
7. References .................................................. 11
7.1. Normative References ................................... 11
7.2. Informative References ................................. 11
8. Acknowledgments ............................................. 12
Authors' Addresses ............................................. 13
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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
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-WIKI]
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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-WIKI]
libxml: a software library for parsing XML documents.
<get-block>: a capability and operation defined in this document to
handle large size
3. Problem Statement
3.1. Current Large size Handling Methods
3.1.1. Stream-Oriented Handling
Stream-Oriented handling mainly includes the following two aspects:
- The server encapsulates the large size replying data in a <rpc-
reply> message and streams it to the client through TCP protocol.
- 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.
3.1.2. 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.
3.2. Problems
o Problems of Stream-Oriented handling
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.
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Another problem is the implementation. SAX is not as widely supported
as DOM [DOM-PARSING]. For example, it is not supported by some
existing libraries such as libxml [LIBXML].
o Problems of subsets request
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.
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. Solution
4.1. Rationale: Standardized RPC Fragmentation Handling
To fix the problems analyzed above, this document proposes an RPC
fragmentation mechanism to handle the large size data. Two essential
requirements of the fragmentation are:
1) 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.
2) 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.
4.2. Design Choice: <get-block> extension
This section introduces the specific extension to current NETCONF
protocol to handle the fragmentation.
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4.2.1. <get-block> Capability
The Get-block capability allows devices to interact with the clients
when getting data. A client sends a <get-config> request, if the
searched data is too big to be encapsulated in one <rpc-reply>, then
the data was fragmented into multiple <rpc-reply> messages. A <rpc-
reply> initial search request ID is included in each fragmented <rpc-
reply>; the client sends a <get-block> operation rpc request to
indicate the server response the next <rpc-reply>, or terminate the
search request in advance.
4.2.2. <get-block> Operation
o Function
The devices can only use <get-block> operation when the Get-block
capability was announced.
The <get-block> fragmentation rules are:
- There should be a Max-Size for fragmentation. [Open Question]Should
there be a clear specification of the size? E.g. 64K bytes.
- When the message reaches the Max-Size, it is sent to the client and
the next message could be created in advance.
- Different records from one same table could be put into different
<rpc-reply> messages
- All of the fields in one record MUST be put into one <rpc-reply>
message.
- XML syntax MUST be complete in each fragmented message, so that
each fragmentation could be parsed individually.
- 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.
Following is an example of the above last rule. The child eTable is
in a different message with the parents aTable->bTable->cTable-
>dTable. Then the path and index information of all the ancestors
MUST included in the search data.
<aTable>
<aEntity>
<aIndex1>
</aEntity>
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<bTable>
<bEntity>
<bIndex1>
</bEntity>
<eTable>
<eEntity>
<eIndex1>
<ef2>
<ef3>
</eEntity>
</dTable>
</bTable>
</aTable>
o Parameters
<discard/>: in <get-block> operation 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 Failed Operation Reply
A <rpc-reply> message conveying a <rpc-error> element indicates the
operation is failed.
o Exception Handling
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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.
4.2.3. Examples
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>
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<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>
</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>
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<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"
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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>
5. Security Considerations
TBD.
6. IANA Considerations
None.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. Bierman,
"Network Configuration Protocol (NETCONF)", RFC 6241, June
2011.
7.2. Informative References
[DOM-WIKI]http://en.wikipedia.org/wiki/Document_Object_Model
[DOM-PARSING]
http://www.w3.org/TR/DOM-Parsing/
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[SAX-WIKI]http://en.wikipedia.org/wiki/Simple_API_for_XML
[SAX-PARSING]
http://www.saxproject.org/apidoc/org/xml/sax/Parser.html
[LIBXML] http://xmlsoft.org/
8. Acknowledgments
Valuable comment was received from Gang Yan and Shouchuan Yang to
form the draft.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Bing Liu
Q14-4-A Building
Huawei Technologies Co., Ltd
Zhong-Guan-Cun Environment Protection Park, No.156 Beiqing Rd.
Hai-Dian District, Beijing
P.R. China
Email: leo.liubing@huawei.com
Guangying Zheng
Q14-4-A Building
Huawei Technologies Co., Ltd
Zhong-Guan-Cun Environment Protection Park, No.156 Beiqing Rd.
Hai-Dian District, Beijing
P.R. China
Email: zhengguangying@huawei.com