NETCONF A. Bierman
Internet-Draft InterWorking Labs
Intended status: Standards Track B. Lengyel
Expires: September 6, 2010 Ericsson
March 5, 2010
With-defaults capability for NETCONF
draft-ietf-netconf-with-defaults-05
Abstract
The NETCONF protocol defines ways to read configuration data from a
NETCONF server. Part of this data is not set by the NETCONF client,
but rather a default value is used. In many situations the NETCONF
client has a priori knowledge about default data, so the NETCONF
server does not need to send it to the client. In other situations
the NETCONF client 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 client to control
whether default values are part of NETCONF <rpc-reply> messages or
<copy-config> output to the target URL.
Status of this Memo
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Copyright Notice
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Current handling of default data . . . . . . . . . . . . . 5
2. With-defaults Capability . . . . . . . . . . . . . . . . . . . 6
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Dependencies . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Conformance . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Capability Identifier . . . . . . . . . . . . . . . . . . 6
2.5. New Operations . . . . . . . . . . . . . . . . . . . . . . 7
2.6. Modifications to Existing Operations . . . . . . . . . . . 7
2.7. Interactions with Other Capabilities . . . . . . . . . . . 9
3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
7. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 13
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 14
B.1. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B.2. 00-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B.3. 01-02 . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B.4. 02-03 . . . . . . . . . . . . . . . . . . . . . . . . . . 14
B.5. 03-04 . . . . . . . . . . . . . . . . . . . . . . . . . . 15
B.6. 04-05 . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
The NETCONF protocol [RFC4741] defines ways to read configuration
data from a NETCONF server. Part of this data is not set by the
NETCONF client, but rather a default value is used. In many
situations the NETCONF client has a priori knowledge about default
data, so the NETCONF server does not need to send it to the client.
A priori knowledge can be e.g., a document formally describing the
data models supported by the NETCONF server.
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 client will need the
default data from the node:
o The management application often needs a single, definitive and
complete set of configuration values that determine how the a
networking device works.
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 these cases the NETCONF client 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 client to control whether default
data is part of NETCONF <rpc-reply> messages.
1.1. Terminology
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].
Data model schema: A document or set of documents describing the
data models supported by the NETCONF server.
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Management Application: A computer program running outside the
NETCONF server that configures or supervises the NETCONF server.
A management application can reach the device e.g. via the
NETCONF, CLI or SNMP.
Default data: Data specified in the data model schema as default,
that is set or used by the device whenever the NETCONF client or
other management application/user does not provide a specific
value for the relevant data item. Default data MAY or MAY NOT be
stored as part of a configuration datastore.
Explicitly set data: Data that is set to any value by a NETCONF
client or other management application by the way of an actual
management operation, including any data model schema default
value. Any value set by the NETCONF server which is not the
schema defined default value is also considered explicitly set
data.
In addition the following terms are defined in RFC 4741 and are not
redefined here:
o client
o operation
o RPC
o RPC request
o RPC response
o server
1.2. Current handling of default data
NETCONF does not define whether default data is part of the
datastore/data model, or if it is meta-data that influences the
behavior of the NETCONF server, but is not actually part of the
datastore. This document is intended to support either type of
implementation, without deciding which approach is better.
As a consequence of this approach, NETCONF servers that do not
implement the :with-defaults capability may or may not return default
data.
Different NETCONF servers report default data in different ways.
This document specifies the following three basic modes:
report-all: All default data is always reported.
trim: Values are not reported if they match the default value (as
specified in the data model schema).
explicit: Report only values that match the definition of explicitly
set data.
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2. With-defaults Capability
2.1. Overview
The :with-defaults capability indicates that the NETCONF server makes
it possible for the NETCONF client to control whether default data is
part of NETCONF <rpc-reply> messages. The capability affects both
configuration and state data (while acknowledging that the usage of
default values for state data is less prevalent). Sending of default
data is controlled for each individual operation separately.
A NETCONF server implementing the :with-defaults capability MUST
indicate its basic behavior, whether it sends default data in the
absence of any specific request from the NETCONF client; and MUST
support the 'report-all' handling mode and MAY support other modes.
A server indicating 'explicit' either in the basic or the also-
supported parameter MUST be able to differentiate between normal
default data and explicitly set data.
2.2. Dependencies
None
2.3. Conformance
Every NETCONF server SHOULD implement this capability.
2.4. Capability Identifier
urn:ietf:params:netconf:capability:with-defaults:1.0
The identifier MUST have a parameter: "basic-mode". This indicates
how the server reports default data in <rpc-reply> messages, in the
case the client 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 1.2.
The identifier MAY have another parameter: "also-supported". This
parameter indicates which additional default handling modes the
server supports. The value of the parameter is a comma separated
list of one or two modes that are supported beside the mode indicated
in the basic parameter. Possible modes are taken from the list in
Section 1.2.
In addition to these parameters, the identifier MUST have the YANG
'module' and 'revision' parameters if the ietf-with-defaults YANG
module is supported, as defined in section 5.6.4 of
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[I-D.ietf-netmod-yang].
Example:
urn:ietf:params:netconf:capability:with-defaults:1.0?module=ietf-
netconf-with-defaults&revision=2010-03-05&basic-mode=report-all
urn:ietf:params:netconf:capability:with-defaults:1.0?module=ietf-
netconf-with-defaults&revision=2010-03-05&basic-mode=report-all&
also-supported=trim,explicit
2.5. New Operations
None
2.6. Modifications to Existing Operations
A new <with-defaults> XML [W3C.REC-xml-20001006] 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 server 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 1.2. The allowed values are restricted to the values that
the device indicates support for in the with-defaults capability in
the basic and also-supported parameters.
If an unsupported value is used, the NETCONF server SHALL return an
<rpc-reply> with an <rpc-error> element. The <error-tag> SHALL be
'operation-not-supported', and the <error-app-tag> SHALL be 'with-
defaults-mode-not-supported'.
If the <with-defaults> element is not present, the server follows its
basic behavior as indicated by the capability identifier's parameter
see Section 2.4.
Affected operations:
o <get>
o <get-config>
o <copy-config>
<copy-config> is only affected if the target of the operation is a
URL. If the target is a NETCONF datastore (running, candidate or
startup) the capability has no effect; the with-defaults parameter,
if present, SHALL be silently ignored.
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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-config> operation which is using
the 'with-defaults' element. The client 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
server 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-config>
<source>
<running/>
</source>
<filter type="subtree">
<interfaces xmlns="http://example.com/interfaces/1.2"/>
</filter>
<with-defaults
xmlns="urn:ietf:params:netconf:capability:with-defaults:1.0">
report-all
</with-defaults>
</get-config>
</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
2.7. Interactions with Other Capabilities
None
3. YANG Module
The following YANG module defines the addition of the with-defaults
element to the <get>, <get-config> and <copy-config> operations. The
YANG language is defined in [I-D.ietf-netmod-yang]. The above
operations are defined in YANG in [I-D.ietf-netconf-4741bis]. Every
NETCONF server SHOULD implement this YANG module.
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-- RFC Ed.: Insert license information for code as appropriate
<CODE BEGINS> file="ietf-netconf-with-defaults.yang"
module ietf-netconf-with-defaults {
namespace "urn:ietf:params:netconf:capability:with-defaults:1.0";
prefix nwd;
import ietf-netconf { prefix nc; }
organization
"IETF NETCONF (Network Configuration Protocol) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Bert Wijnen
<mailto:bertietf@bwijnen.net>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nsn.com>
Editor: Andy Bierman
<mailto:andyb@iwl.com>
Editor: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module defines a capability-based extension to the
NETCONF protocol that allows the NETCONF client to control
whether default values are part of NETCONF
<rpc-reply> messages or <copy-config> output to the target URL.
Copyright (c) 2010 IETF Trust and the persons identified as
the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
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(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with actual RFC number and remove this note
// RFC Ed.: remove this note
// Note: extracted from draft-ietf-netmod-with-defaults-05.txt
revision 2010-03-05 {
description
"Initial version.";
reference
"RFC XXXX: With-defaults capability for NETCONF";
}
// RFC Ed.: replace XXXX with actual RFC number and remove this note
typedef with-defaults-mode {
description
"Possible modes to report default data in
rpc-reply messages.";
type enumeration {
enum report-all {
description
"All default data is always reported.";
}
enum trim {
description
"Values are not reported if they match the default.";
}
enum explicit {
description
"Report values that match the definition of
explicitly set data.";
}
}
}
grouping with-defaults-parameters {
leaf with-defaults {
description
"The explicit defaults processing mode requested.";
type with-defaults-mode;
}
}
// extending the get-config operation
augment /nc:get-config/nc:input {
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uses with-defaults-parameters;
}
// extending the get operation
augment /nc:get/nc:input {
uses with-defaults-parameters;
}
// extending the copy-config operation
augment /nc:copy-config/nc:input {
uses with-defaults-parameters;
}
}
<CODE ENDS>
4. IANA Considerations
This document registers one capability identifier URN from the
'Network Configuration Protocol [RFC4741] Capability URNs' registry,
and registers the same URN 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 |
+---------------+---------------------------------------------------+
5. 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 gives client control 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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6. Acknowledgements
Thanks to Martin Bjorklund, Sharon Chisholm, Phil Shafer, Juergen
Schoenwaelder, Washam Fan and many other members of the NETCONF WG
for providing important input to this document.
7. Normative References
[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.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[I-D.ietf-netconf-4741bis]
Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)",
draft-ietf-netconf-4741bis-02 (work in progress),
February 2010.
[I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for
NETCONF", draft-ietf-netmod-yang-11 (work in progress),
February 2010.
[W3C.REC-xml-20001006]
Sperberg-McQueen, C., Maler, E., Paoli, J., and T. Bray,
"Extensible Markup Language (XML) 1.0 (Second Edition)",
World Wide Web Consortium FirstEdition REC-xml-20001006,
October 2000,
<http://www.w3.org/TR/2000/REC-xml-20001006>.
Appendix A. Open Issues
This section will be removed. The open issues are closed in this
revision of the draft, pending working group approval.
Is the definition of defaults OK? [The definition of explicitly set
default data has been changed to 'explicitly set data', and now
aligns with the YANG definition.]
Shall we wait for YANG and 4741bis and make the YANG normative?
[Yes.]
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Shall we make with-defaults mandatory? [No. It is SHOULD, not
MUST.]
Appendix B. Change Log
-- RFC Ed.: remove this section before publication.
B.1. -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.
B.2. 00-01
Changed value set of with-default capability and element
Added version to URI
B.3. 01-02
report-all made mandatory
Placeholder for YAM added, XSD will be removed when 4741 provides the
NETCONF YAM
with-defaults is valid for state data as well (if state data has a
defined default which might not be so frequent). The definition of
explicit was modified for state data.
B.4. 02-03
Clarifications
YAM added
Use the same URN for the capability and the XML namespace to
accommodate YANG, and avoid two separate URN/URIs being advertised in
the HELLO message, for such a small function.
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B.5. 03-04
Clarifications
Added non-netconf interfaces to the definition of explicitly set
default data
B.6. 04-05
Updated I-D and YANG module boiler-plate.
Removed redundant 'with-defaults' YANG feature.
Changed definition of 'explicit' mode to match the YANG definition
Removed XSD because the YANG is normative and the XSD is
unconstrained, and does not properly extend the 3 affected NETCONF
operations.
Made the YANG module a normative section instead of non-normative
appendix.
Changed YANG from an informative to a normative reference,
Changed 4741bis from an informative to a normative reference because
the YANG module imports the ietf-netconf module in order to augment
some RPC operations.
Updated capability requirements to include YANG module capability
parameters.
Added a description statement to the with-defaults leaf definition.
Update open issues section; ready to close all open issues.
Authors' Addresses
Andy Bierman
InterWorking Labs
303 Potrero Street, Suite 52
Santa Cruz, CA 95060-2760
USA
Phone: +1 831 460 7010
Email: andyb@iwl.com
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Balazs Lengyel
Ericsson
Budapest,
Hungary
Email: balazs.lengyel@ericsson.com
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