NETCONF A. Bierman
Internet-Draft Netconf Central
Intended status: Standards Track B. Lengyel
Expires: October 8, 2009 Ericsson
April 06, 2009
With-defaults capability for NETCONF
draft-ietf-netconf-with-defaults-01
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Abstract
The NETCONF protocol defines ways to read configuration data from a
NETCONF agent. Part of this data is not set by the NETCONF manager,
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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 . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Other default handling methods in the real world? . . . . 10
7.2. XSD needed? . . . . . . . . . . . . . . . . . . . . . . . 10
8. Appendix A - Change Log . . . . . . . . . . . . . . . . . . 11
8.1. 00-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.2. -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:1.0
The identifier MUST have a 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 listed in Section 2.1.1.
The identifier MAY have another parameter: "supported". This
indicates what other default handling methods does the agent support.
The value of the parameter is a colon separated list of one or two
supported methods. Possible methods are taken from the list in
Section 2.1.1.
Example:
urn:ietf:params:netconf:capability:with-defaults:1.0?basic=report-all
urn:ietf:params:netconf:capability:with-defaults:1.0?basic=report-
all&supported=trim:explicit
2.4. New Operations
None
2.5. Modifications to Existing Operations
A new <with-defaults> XML child 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 taken from the list
in Section 2.1.1. The allowed values are restricted to the values
that the device indicates support for in the with-defaults
capability.
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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.
Affected operations:
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 'report-all',
the mtu is returned not just for eth0 but also for eth1.
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<rpc message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<get>
<with-defaults>report-all</with-defaults>
<filter type="subtree">
<interfaces xmlns="http://example.com/interfaces/1.2"/>
</filter>
</get>
</rpc>
<rpc-reply message-id="102"
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>
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.
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<?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:attribute name="with-defaults" >
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="report-all"/>
<xs:enumeration value="trim"/>
<xs:enumeration value="explicit"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</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.
+---------------+---------------------------------------------------+
| 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?
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8. Appendix A - Change Log
8.1. 00-01
Changed value set of with-default capability and element
Added version to URI
8.2. -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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