One document matched: draft-bierman-netconf-with-defaults-01.xml
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<rfc category="std" docName="draft-bierman-netconf-with-defaults-01" ipr="full3978">
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<front>
<title abbrev="with-defaults">
With-defaults capability for NETCONF
</title>
<author fullname="Andy Bierman" initials="A.B."
surname="Bierman">
<organization>Netconf Central</organization>
<address>
<postal>
<street></street>
<city>Simi Valley</city>
<region>CA</region>
<code></code>
<country>USA</country>
</postal>
<email>andy@netconfcentral.com</email>
</address>
</author>
<author fullname="Balazs Lengyel" initials="B. L."
surname="Lengyel">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<city>Budapest</city>
<region></region>
<code></code>
<country>Hungary</country>
</postal>
<email>balazs.lengyel@ericsson.com</email>
</address>
</author>
<date year="2008" month="October" day="22"/>
<area>OPS</area>
<workgroup>NETCONF</workgroup>
<keyword>with-defaults</keyword>
<keyword>XML</keyword>
<abstract>
<t>
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. 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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
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.
<vspace blankLines="1"/>
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.
<vspace blankLines="1"/>
However there are use-cases when a NETCONF manager
will need the default data from the node:
<vspace blankLines="1"/>
<list style="symbols">
<t>Documentation about default values can be unreliable or unavailable.</t>
<t>Some management applications might not have the capabilities to
correctly parse and interpret formal data models.</t>
<t>Human users might want to understand the received
data without consultation of the documentation.</t>
</list>
<vspace blankLines="1"/>
In all theses cases the NETCONF manager will need default data as part of the NETCONF rpc reply messages.
<vspace blankLines="1"/>
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.
</t>
<section title="Terminology">
<section title="Requirements Notation">
<t>
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 <xref target="RFC2119"/>.
</t>
</section>
<section title="NETCONF Terms" anchor="NetconfTerms">
<t>
<list style="symbols">
<t>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. In the context of this document only
configuration data is considered, state data is excluded.
<vspace blankLines="1"/>
</t>
<t>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.</t>
</list>
</t>
<t>
In addition the following terms are defined in RFC 4741 and are not redefined here:
<list style="symbols">
<t>agent</t>
<t>application</t>
<t>manager</t>
<t>operation</t>
<t>RPC</t>
<t>RPC request</t>
<t>RPC response</t>
</list>
</t>
</section>
</section>
</section>
<section title="With-defaults Capability">
<section title="Overview"><t>
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 effects configuration data
not state data. Sending of default data is controlled for each individual operation separately.
The NETCONF agent MUST also indicate it's basic behavior, whether it sends default data in
the absence of any specific request from the NETCONF manager.
<vspace blankLines="1"/>
This capability effects the <get>, <get-config> and <copy-config> operations. Other operations that MIGHT return
configuration data are not effected, unless this is specified in the document defining the respective operation.
</t>
<section title="Basic handling of default data" anchor="basicHandling">
<t>
It is not defined in <xref target="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.
<vspace blankLines="1"/>
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.
<vspace/>
Management agents report default data in different ways. This document specifies the following three basic methods:
<list style="symbols">
<t>Report all: All default data is always reported.</t>
<t>Trim: Values are not reported if they match the default.</t>
<t>Explicit: Report values if they are explicitly set.</t>
</list>
</t>
</section>
</section>
<section title="Dependencies"><t>None</t></section>
<section title="Capability Identifier" anchor="capabilityIdChapter">
<t>
urn:ietf:params:netconf:capability:with-defaults
<vspace blankLines="1"/>
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 <xref target="basicHandling"/>. E.g.:
<vspace blankLines="1"/>
urn:ietf:params:netconf:capability:with-defaults?basic=report-all
</t>
</section>
<section title="New Operations"><t>None</t></section>
<section title="Modifications to Existing Operations">
<t>
A new 'with-defaults' XML attribute is used
to control the reporting of default data.
If the 'with-defaults' attribute is present in the <rpc>
element of the affected operations, the agent MUST return
default data in the NETCONF rpc reply messages according to the value of the attribute.
</t>
<t>
Allowed values of the with-defaults attribute are:
<list style="symbols">
<t>false: indicates that default data will be returned as if the
manager has omitted the attribute, using its basic handling
method for defaults. The basic
behavior is indicated by the attribute on the capability.
See <xref target="capabilityIdChapter"/></t>
<t>true: indicates that all default data MUST be returned.</t>
</list>
</t>
<t>
The 'with-defaults' attribute is defined in the
namespace specified as the 'targetNamespace' in
<xref target="XSD"/>. However, an agent MUST
accept it even if no namespace is used.
</t>
</section>
<t>
Affected operations:
<list style="symbols">
<t><get></t>
<t><get-config></t>
<t><copy-config></t>
</list>
</t>
<t>
The following example shows a <get> operation
which is using the 'with-defaults' attribute.
The manager is retrieving the 'interfaces' object,
defined in the example.com Interfaces 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'
attribute is set to 'true', the mtu is returned not just for eth0 but also for eth1.
</t>
<t>
<figure anchor="with_defaults_example">
<artwork>
<![CDATA[
<rpc message-id="102" with-defaults="true"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get>
<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>
]]>
</artwork>
</figure>
</t>
</section>
<section title="Interactions with Other Capabilities"><t>None</t></section>
<section title="Data Model XSD" anchor="XSD">
<t>
This section contains an XML Schema Definition
<xref target="W3C.REC-xmlschema-2-20041028"/> which
defines the XML syntax associated for the with-defaults XML attribute.
</t>
<t>
<figure>
<artwork>
<![CDATA[
<?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 attribute.
Organization: "IETF NETCONF Working Group"
Contact Info: balazs.lengyel@ericsson.com
</xs:documentation>
</xs:annotation>
<xs:attribute name="with-defaults"
type="xs:boolean"/>
</xs:schema>
]]>
</artwork>
</figure>
</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document registers two URIs for the NETCONF XML namespace in
the IETF XML registry <xref target="RFC3688"></xref>. Note that the capability URN is compliant to
<xref target="RFC4741"></xref> section 10.3.</t>
<texttable>
<ttcol align="left" width="20%">Index</ttcol>
<ttcol align="left">Capability Identifier</ttcol>
<c>:with-defaults</c>
<c>urn:ietf:params:netconf:capability:with-defaults:1.0</c>
</texttable>
<?rfc compact="no"?>
<t>URI: urn:ietf:params:xml:ns:netconf:with-defaults:1.0
<vspace blankLines="1"/>
Registrant Contact: The IESG.
<vspace blankLines="1"/>
XML: N/A, the requested URI is an XML namespace.
</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>
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.
</t>
<t>
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.
</t>
</section>
<section title="Open Issues">
<section title="Augmenting the base RPCs">
<t>
Instead of using an attribute on the RPC element we could "augment" the relevant
NETCONF operations with an extra XML element with a similar meaning.
<vspace blankLines="1"/>
Pro: parameters on RPC are for vendor extensions. We should not put standard stuff there.
<vspace blankLines="1"/>
Contra: Some people might consider this a violation of <xref target="RFC4741"/> as the
XSD does not allow adding new elements. As there is no NETCONF YAM (at least not yet), what do
we actually augment? Also there are multiple ways of defining RFC4741 in YANG.
The description will be perfectly clear, but it can never be fed into YANG tools.
<vspace blankLines="1"/>
Conclusion: While augmenting has a certain elegance, we should stick to the attribute based solution.
</t>
</section>
<section title="Other default handling methods in the real world?">
<t>
Are there any other basic default handling methods out there we need to include?
</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
&xsdspec;
<reference anchor='RFC4741'>
<front>
<title>NETCONF Configuration Protocol</title>
<author initials='R.' surname='Enns' fullname='R. Enns'>
<organization /></author>
<date year='2006' month='December' />
<abstract>
<t>The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized on top of a simple Remote Procedure Call (RPC) layer. [STANDARDS TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='4741' />
<format type='TXT' octets='173914' target='ftp://ftp.isi.edu/in-notes/rfc4741.txt' />
</reference>
<reference anchor='RFC2119'>
<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street></postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email></address></author>
<date year='1997' month='March' />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>
In many standards track documents several words are used to signify
the requirements in the specification. These words are often
capitalized. This document defines these words as they should be
interpreted in IETF documents. Authors who follow these guidelines
should incorporate this phrase near the beginning of their document:
<list>
<t>
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
RFC 2119.
</t></list></t>
<t>
Note that the force of these words is modified by the requirement
level of the document in which they are used.
</t></abstract></front>
<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='ftp://ftp.isi.edu/in-notes/rfc2119.txt' />
<format type='HTML' octets='17491' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5777' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>
<reference anchor='RFC3688'>
<front>
<title>The IETF XML Registry</title>
<author initials='M.' surname='Mealling' fullname='M. Mealling'>
<organization /></author>
<date year='2004' month='January' />
<abstract>
<t>This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas.</t></abstract></front>
<seriesInfo name='BCP' value='81' />
<seriesInfo name='RFC' value='3688' />
<format type='TXT' octets='17325' target='ftp://ftp.isi.edu/in-notes/rfc3688.txt' />
</reference>
</references>
</back>
</rfc>
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