One document matched: draft-bierman-netconf-with-defaults-00.txt
NETCONF A. Bierman
Internet-Draft netconfcentral.org
Intended status: Standards Track B. Lengyel
Expires: February 28, 2009 Ericsson
August 27, 2008
With-defaults capability for NETCONF
draft-bierman-netconf-with-defaults-00
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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,
but rather set to a default value by the NETCONF agent. In many
situations the NETCONF manager has a priori knowledge about this
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-
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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. Augmenting the base RPCs . . . . . . . . . . . . . . . . . 10
7.2. Third option: Trim . . . . . . . . . . . . . . . . . . . . 10
7.3. List affected operations or generalize . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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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 set to a default value by the NETCONF agent. In many
situations the NETCONF manager has a priori knowledge about this
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. It is quite common for
networking devices to suppress the output of parameters set to the
default value. This is done to save CPU time and non-volatile
memory. In addition, there are likely to be a large number of such
parameters. Is is often not useful for network operators to view all
these default values. It is usually more interesting to view just
the parameters which have been explicitly set by the network
operator.
However there are perfectly valid use-cases when a NETCONF manager
will need the default data from the node. Documentation about
default values is often unreliable or unavailable. Some management
applications might not have the capabilities to correctly parse and
interpret formal data models. Human users might want to understand
the received data without extensive 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 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.
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 default data, as they might not be
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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 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 default behavior, whether it sends
default data in the absence of any specific request from the NETCONF
manager.
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.
TODO: what about model defined RPCs? Will they be effected? How can
it be stated in YANG whether yes or no?
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 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. The described functionality should work in both cases.
As a consequence of this issue basic NETCONF servers that do not
implement the :with-defaults capability may or may not return default
data in NETCONF rpc reply messages.
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2.2. Dependencies
None
2.3. Capability Identifier
urn:ietf:params:netconf:capability:with-defaults
The identifier MUST have an additional parameter indicating the
default value of with-defaults for the NETCONF agent. The allowed
values of with-defaults attribute can be used as a default value see
Section 2.5.
urn:ietf:params:netconf:capability:with-defaults?default=false
The identifier MAY have a second parameter indicating how it treats
explicitly set default data. If the explicit-default parameter is
set to "unrecognized" the agent MUST treat explicitly set default
data as normal default data. If the parameter is set to recognized
this means that such data is not treated as default data. All other
values for the parameter or a missing parameter is handled as the
value unrecognized.
urn:ietf:params:netconf:capability:with-defaults?default=false&
explicit-default=recognized
2.4. New Operations
None
2.5. Modifications to Existing Operations
A new 'with-defaults' XML attribute is used to control the generation
of default data. If the 'with-defaults' attribute is present in the
<rpc> element, of the affected operations, the agent will use it's
value to control whether default data is returned in the NETCONF rpc
reply messages.
Allowed values of the with-defaults attribute are:
o true: indicates that all default data MUST be returned.
o false: indicates that default data MUST NOT be returned.
The 'with-defaults' attribute is defined in the namespace specified
as the 'targetNamespace' in Section 4. However, an agent should
accept it even if no namespace is used.
If the 'with-defaults' attribute is not present it's default value as
specified in the capability string Section 2.3 will be used.
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Affected operations:
o <get>
o <get-config>
o <copy-config>
Index clause components are not subject to default suppression. If
an element within the configuration database is considered to be part
of a key, and represents one of the naming components for a
conceptual data structure which allows multiple named instances of an
ancestor node, then this element is never suppressed, regardless of
the value of the 'with-defaults' attribute.
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 MTU value of '1500' is not returned for the
interface named 'Eth1' because it is set to the default value, and
the 'with-defaults' attribute is set to 'false'.
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<rpc message-id="102" with-defaults="false"
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="false"
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>
</interface>
<interface>
<name>loopback</name>
<mtu>8192</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 attribute..
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BEGIN
<?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" version="1.0" >
<xs:annotation>
<xs:documentation>
Schema defining the partial-lock and unlock operations.
organization "IETF NETCONF Working Group"
Version: 1.0
Contact Info: ietf@andybierman.com
balazs.lengyel@ericsson.com
</xs:documentation>
</xs:annotation>
<xs:attribute name="with-defaults"
type="xs:boolean"/>
</xs:schema>
END
Figure 2
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. Augmenting the base RPCs
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.
Pro: parameters on RPC are for vendor extensions. We should not put
standard stuff there.
Contra: Some people might consider this a violation of [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.
Conclusion: While augmenting has a certain elegance, we should stick
to the attribute based solution.
7.2. Third option: Trim
This is another can o' worms. I preserve user specified values even
when the value matches the default. This allows users complete
control over what appears in their config. Values to not disappear
simply because the match the default.
If you want this behavior, I'd suggest making your "with-defaults" a
tri-state value:
"all" -- report all default values
"trim" -- do not report values if they match the default
"explicit" -- report any values explicitly set
Do we need the trim option ?
7.3. List affected operations or generalize
Should we list affected operations <get>, <get-config>, <copy-config>
or should we just say "any of the protocol operations which return
the contents of a configuration database", or should we do both?
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8. 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
netconfcentral.org
Simi Valley, CA
USA
Email: ietf@andybierman.com
Balazs Lengyel
Ericsson
Hungary
Email: balazs.lengyel@ericsson.com
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