NETCONF A. Bierman
Internet-Draft Netconf Central
Intended status: Standards Track B. Lengyel
Expires: April 25, 2010 Ericsson
October 22, 2009
With-defaults capability for NETCONF
draft-ietf-netconf-with-defaults-04
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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,
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Current handling of default data . . . . . . . . . . . . . 4
2. With-defaults Capability . . . . . . . . . . . . . . . . . . . 5
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Dependencies . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Capability Identifier . . . . . . . . . . . . . . . . . . 5
2.4. New Operations . . . . . . . . . . . . . . . . . . . . . . 6
2.5. Modifications to Existing Operations . . . . . . . . . . . 6
3. Interactions with Other Capabilities . . . . . . . . . . . . . 7
4. Data Model XSD . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Appendix A - YANG Module for with-defaults (non-normative) . 9
9. Appendix B - Change Log . . . . . . . . . . . . . . . . . . 12
9.1. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.2. 00-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.3. 01-02 . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.4. 02-03 . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.5. 03-04 . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
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. 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].
o Data model schema is a document or set of documents describing the
data models supported by the NETCONF server.
o 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 external management application/user does not provide a
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specific value for the relevant data item. External management
application/user can reach the device e.g. via the NETCONF, CLI,
SNMP, GUI. Default data MAY or MAY NOT be stored as part of a
configuration datastore.
o Explicitly set default data: Is default data that is set by a
NETCONF client or other external management application/user by
the way of an actual management operation to the value specified
as its default in the data model schema. Some servers MAY treat
explicitly set default data as simple default data, as they may
not be able to differentiate between them.
Data, that is set to a value other then its default value, is not
default data, so its handling is outside the scope of this
document.
In addition the following terms are defined in RFC 4741 and are not
redefined here:
o application
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 issue, 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:
o report-all: All default data is always reported.
o trim: Values are not reported if they match the default.
o explicit: Default data is not reported except explicitly set
default data. For state data this has the same effect as report-
all.
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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 default data.
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 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.
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&also-supported=trim,explicit
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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 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 a not allowed value is used the NETCONF server SHALL return an
<rpc-reply> with an <rpc-error> element. The <error-tag> SHALL be
'operation-not-supported', the <error-app-tag> SHALL be "with-
defaults-mode-not-supported', and <error-info> SHALL contain the
requested mode.
If the <with-defaults> element is not present, the server follows its
basic behavior as indicated by the capability identifier's parameter
see Section 2.3.
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.
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'
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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.
<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
3. Interactions with Other Capabilities
None
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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.
-- RFC Ed.: Insert license information for code as appropriate
<CODE BEGINS>
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns="urn:ietf:params:netconf:capability:with-defaults:1.0"
targetNamespace="urn:ietf:params:netconf:capability: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:element 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:element>
</xs:schema>
<CODE ENDS>
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5. IANA Considerations
This document registers one capability identifier URN from the
"Network Configuration Protocol [NETCONF] 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 [NETCONF] section 10.3.
+---------------+---------------------------------------------------+
| Index | Capability Identifier |
+---------------+---------------------------------------------------+
| :with-default | urn:ietf:params:netconf:capability:with-defaults: |
| s | 1.0 |
+---------------+---------------------------------------------------+
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 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.
7. Open Issues
Is the definition of defaults OK?
Shall we wait for YANG and 4741bis and make the YANG normative?
Shall we make with-defaults mandatory?
8. Appendix A - YANG Module for with-defaults (non-normative)
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].
-- RFC Ed.: Insert license information for code as appropriate
<CODE BEGINS>
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module ietf-netconf-with-defaults {
namespace "urn:ietf:params:netconf:capability:with-defaults:1.0";
prefix nwd;
// for the uri data type
import ietf-netconf { prefix nc; }
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) 2009 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, are permitted provided that the
following conditions are met:
- Redistributions of source code must retain the above
copyright notice, this list of conditions and the
following disclaimer.
- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other
materials provided with the distribution.
- Neither the name of Internet Society, IETF or IETF
Trust, nor the names of specific contributors, may be
used to endorse or promote products derived from this
software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
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
reference "RFC XXXX";
// RFC Ed.: replace XXXX with actual RFC number and remove this note
// reference "draft-ietf-netconf-with-defaults-03.txt";
// RFC Ed.: remove the reference statement above and this note.
contact
"Send comments to the NETCONF WG mailing list.
<netconf@ietf.org>";
revision 2009-07-01 {
description
"Initial version";
}
// with-defaults capability defined as a feature
feature with-defaults {
description
"NETCONF :with-defaults capability;
If the server advertises the :with-defaults
capability for a session, then this feature MUST
also be enabled for that session. Otherwise,
this feature MUST NOT be enabled.";
// RFC Ed.: replace XXXX with actual RFC number and
// remove this note
reference "RFC XXXX";
}
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 {
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description
"Values are not reported if they match the default.";
}
enum explicit {
description
"Report values if they are explicitly set.
For state data this has the same effect
as report-all";
}
}
}
// extending the get-config operation
augment /nc:get-config/nc:input {
leaf with-defaults {
type with-defaults-mode;
}
}
// extending the get operation
augment /nc:get/nc:input {
leaf with-defaults {
type with-defaults-mode;
}
}
// extending the copy-congig operation
augment /nc:copy-config/nc:input {
leaf with-defaults {
type with-defaults-mode;
}
}
}
<CODE ENDS>
9. Appendix B - Change Log
9.1. -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
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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.
9.2. 00-01
Changed value set of with-default capability and element
Added version to URI
9.3. 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.
9.4. 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.
9.5. 03-04
Clarifications
Added non-netconf interfaces to the definition of explicitly set
default data
10. 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.
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11. References
11.1. 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>.
[NETCONF] 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.
11.2. Informative References
[I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for
NETCONF", draft-ietf-netmod-yang-08 (work in progress),
October 2009.
[I-D.ietf-netconf-4741bis]
Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "NETCONF Configuration Protocol",
draft-ietf-netconf-4741bis-01 (work in progress),
July 2009.
Authors' Addresses
Andy Bierman
Netconf Central
Simi Valley, CA
USA
Email: andy@netconfcentral.com
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Balazs Lengyel
Ericsson
Budapest,
Hungary
Email: balazs.lengyel@ericsson.com
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