NETCONF B. Lengyel
Internet-Draft Ericsson Hungary
Intended status: Standards Track M. Bjorklund
Expires: December 15, 2008 Tail-f Systems
June 13, 2008
Partial Lock RPC for NETCONF
draft-ietf-netconf-partial-lock-02
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Copyright (C) The IETF Trust (2008).
Abstract
The NETCONF protocol defines the lock and unlock RPCs that lock
entire configuration datastores. In some situations, a way to lock
only parts of a configuration datastore is required. This document
defines a capability-based extension to the NETCONF protocol for
locking portions of a configuration datastore.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 3
2. Partial Locking Capability . . . . . . . . . . . . . . . . . . 3
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Dependencies . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Capability Identifier . . . . . . . . . . . . . . . . . . 4
2.4. New Operations . . . . . . . . . . . . . . . . . . . . . . 4
2.4.1. <partial-lock> . . . . . . . . . . . . . . . . . . . . 4
2.4.2. <partial-unlock> . . . . . . . . . . . . . . . . . . . 8
2.5. Modifications to Existing Operations . . . . . . . . . . . 9
2.6. Interactions with Other Capabilities . . . . . . . . . . . 9
2.6.1. Writable-Running Capability . . . . . . . . . . . . . 9
2.6.2. Candidate Configuration Capability . . . . . . . . . . 9
2.6.3. Distinct Startup Capability . . . . . . . . . . . . . 9
3. Security Considerations . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Appendix A - XML Schema for Partial Locking (normative) . . 11
6. Appendix B - YANG Module for Partial Locking
(non-normative) . . . . . . . . . . . . . . . . . . . . . . . 13
7. Appendix C - Change Log . . . . . . . . . . . . . . . . . . 15
7.1. 01-02 . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.2. 00-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.3. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19
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1. Introduction
The NETCONF protocol [NETCONF] describes the lock and unlock RPCs
that operate on entire configuration datastores. Often, multiple
management sessions need to be able to modify the configuration of a
managed device in parallel. In these cases, locking only parts of a
configuration datastore is needed. This document defines an
extension to the NETCONF protocol to allow this.
The mechanism for partial locking is based on the existing XPath
filtering mechanisms.
Partial locking is defined as a capability to NETCONF.
1.1. Definition of Terms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14, [RFC2119].
2. Partial Locking Capability
2.1. Overview
The :partial-lock capability indicates that the device supports the
locking of its configuration with a scope smaller then a complete
configuration datastore. The scope to be locked is specified by
using restricted or full XPath expressions. Partial locking covers
configuration data, but not state data.
The system MUST ensure that configuration resources covered by the
lock are not modified by other NETCONF or non-NETCONF management
operations such as SNMP and the CLI.
The duration of the partial lock is defined as beginning when the
partial lock is granted and lasting until either the corresponding
<partial-unlock> operation succeeds or the NETCONF session
terminates.
A NETCONF session MAY have multiple parts of one or more datastores
(running, candidate,startup) locked using partial lock operations.
The <partial-lock> operation returns a lock-id to identify each
successfully acquired lock.
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2.2. Dependencies
The device MUST support the restricted XPath expressions in the
select element, as described in Section 2.4.1 If optionally the
:xpath capability is also supported, the device MUST also support the
usage of any XPath 1.0 expression in the select element.
2.3. Capability Identifier
urn:ietf:params:netconf:capability:partial-lock:1.0
2.4. New Operations
2.4.1. <partial-lock>
The <partial-lock> operation allows the client to lock a portion of a
data store. The portion to lock is specified by using XPath
expressions in the select elements of the <partial-lock> operation.
Each XPath expression MUST return a node set.
The select XPath expressions are evaluated only once at lock time,
thereafter the scope of the lock is maintained as a set of nodes. If
the configuration data is later altered in a way that would make the
original select XPath expressions evaluate to a different set of
nodes, this does not affect the scope of the partial lock.
XPath is only used for the creation of the partial lock.
Conceptually the scope of the lock is defined by the returned node
set and not by the XPath expression.
A <partial-lock> operation MUST be handled atomically by the NETCONF
server. The server either locks all requested parts of the data
store or none; I.e. if during the operation one of the requested
parts cannot be locked the server MUST unlock all parts that have
been already locked during that operation.
If a node is locked by a session, only that same session is able to
modify that node or any node in the subtree underneath it.
If a top level node of a locked subtree is deleted, any other session
can recreate it, as it is not covered by the lock anymore. If all
top level nodes are deleted, the lock will still be present, however
it's scope will become nil i.e. it will not cover any nodes.
A partial lock MUST fail if:
o Any NETCONF session (including the current session) owns the
global lock on the datastore.
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o Any part of the scope to be locked is already locked by another
management session/protocol, including other NETCONF sessions
using the <partial-lock> or any other non-NETCONF management
method.
o The NETCONF server implements access control and the locking user
does not have sufficient privileges, to all parts of the datastore
section to be locked. The exact handling of access rights is
outside the scope of this document, but it is assumed that there
is an access control system that MAY deny or allow the partial
lock operation.
Note: If partial lock is requested for the running datastore, and the
NETCONF server implements the :confirmed-commit capability, and there
was a recent confirmed <commit> operation, where the confirming
<commit> operation has not been received. In this case the lock MUST
be denied, because if the confirmation does not arrive, the running
datastore MUST be rolled back to its state before the commit, thus
the NETCONF server might need to modify the configuration.
As with most locking systems, there is a possibility that two
management sessions trying to lock different parts of the
configuration become dead-locked. To avoid this situation, clients
SHOULD lock everything they need in one operation. If that operation
still fails, the client SHOULD back down, release any already
acquired locks, and retry the procedure after some time interval.
The length of the interval should preferably be random to avoid
repeated dead-locks when both (or all) clients back down and then
repeat locking.
It is the intention to keep partial-locking simple, so when a partial
lock is executed you get what you asked for: a set of nodes that are
locked for writing. There are some other issues that are
intentionally not addressed for the sake of simplicity:
o Locking does not affect read operations.
o If a part of a datastore is locked, this has no effect on any
unlocked parts of the datastore. If this is a problem e.g. the
operator's changes depend on data values in the unlocked part of
the datastore, the operator should include these values in the
scope of the lock.
o An operator is allowed to edit the configuration both inside and
outside the scope of a lock. It is the operator's responsibility
to lock all parts of the datastore that are crucial for a specific
management action.
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Note: The <partial-lock> operation does not modify the global <lock>
operation defined in the base NETCONF Protocol [NETCONF]. If part of
a datastore is already locked by <partial-lock>, then a global lock
for that datastore fails even if the global lock is attempted by the
same NETCONF session which owns the partial-lock.
Parameters:
target: Name of the configuration datastore of which a part shall be
locked. One <partial-lock> operation can affect only one of the
datastores. URLs are not accepted.
select: One or more 'select' elements each containing an XPath
expression. The XPath expression is evaluated in a context where
the context node is the root of the server's conceptual data
model, and the set of namespace declarations are those in scope
on the select element.
The select expressions MUST each return a node set, and at least
one of the node sets must be non-empty.
If the device supports the :xpath capability as well any valid
XPath 1.0 expression can be used, if not, the XPath expression
MUST be limited to an Instance Identifier expression. An
Instance Identifier is an absolute path expression in abbreviated
syntax, where predicates are used only to specify values for
nodes defined as keys to distinguish multiple instances.
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Example: Lock virtual router 1 and interface eth1
<nc:rpc
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns="urn:ietf:params:xml:ns:netconf:partial-lock:1.0"
xmlns:rte="http://example.com/ns/route">
xmlns:if="http://example.com/ns/interface">
nc:message-id="135">
<partial-lock>
<nc:running/>
<select>/routing/virtualRouter['routerName=router1']</select>
<select>/interfaces/interface[Id='eth1']</select>
</partial-lock>
</nc:rpc>
<nc:rpc-reply
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns="urn:ietf:params:xml:ns:netconf:partial-lock:1.0"
xmlns:rte="http://example.com/ns/route">
xmlns:if="http://example.com/ns/interface">
nc:message-id="135">
<nc:data>
<lock-id>127</lock-id>
</nc:data>
</nc:rpc-reply>
Positive Response:
If the device was able to satisfy the request, an <rpc-reply> is sent
with a <lock-id> element (lock identifier) in the <data> element.
Negative Response:
If a lock is already held on any node within the subtrees to be
locked, the <error-tag> element is 'lock-denied' and the <error-info>
element includes the <session-id> of the lock owner. If the lock is
held by a non-NETCONF entity, a <session-id> of 0 (zero) is included.
If the select expressions return an empty node set, the <error-tag>
is 'operation-failed', and the <error-app-tag> is 'no-matches'.
If any select expression returns anything but a node set, the <error-
tag> is 'invalid-value', the <error-app-tag> is 'XPath does not
return a node set'.
If the :xpath capability is not supported and the XPath expression is
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not an Instance Identifier, the <error-tag> is 'invalid-value', the
<error-app-tag> is ':xpath capability not supported'.
If access control denies the partial lock, the <error-tag> is
'access-denied'.
2.4.1.1. Reserving model sections for future work
Partial lock can not be used to lock non-existing nodes, effectively
reserving them for future use. To make sure that a node cannot be
created by some other session, the parent node should be locked, the
top level node of the new section created, and then locked with
another <partial-lock> operation. After this the lock on the parent
node should be removed.
2.4.2. <partial-unlock>
The operation unlocks a part of a datastore that was previously
locked using <partial-lock> during the same session.
Parameters:
lock-id: Lock identifier to unlock; taken from a reply to a previous
<partial-lock> operation.
Example: Unlock
<nc:rpc xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns="urn:ietf:params:xml:ns:netconf:partial-lock:1.0"
nc:message-id="136">
<partial-unlock>
<lock-id>127</lock-id>
</partial-unlock>
</nc:rpc>
Positive Response:
If the device was able to satisfy the request, an <rpc-reply> is sent
that contains an <ok> element. A positive response MUST be sent even
if all of the locked part of the datastore has already been deleted.
Negative Response:
If the <lock-id> parameter does not identify a lock which is owned by
the session, an 'invalid-value' error is returned.
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2.5. Modifications to Existing Operations
A granted partial-lock will cause operations that want to modify the
locked area to fail, if executed in a NETCONF session other then the
one that owns the lock. Affected operations include: <edit-config>,
<copy-config>, <delete-config>, <commit> and <discard-changes>. A
granted partial-lock will also cause the (global) <lock> operation to
fail. All of these operations are affected only if they are for the
same datastore.
2.6. Interactions with Other Capabilities
2.6.1. Writable-Running Capability
Partial locking of the running datastore can only be done if the
:writable-running capability is supported by the device.
2.6.2. Candidate Configuration Capability
Partial locking of the candidate datastore can only be done if the
:candidate capability is supported by the device. The partial
locking of the candidate datastore does not depend on whether the
datastore was modified or not.
2.6.3. Distinct Startup Capability
Partial locking of the startup datastore can only be done if the
:startup capability is supported by the device.
3. Security Considerations
The same considerations as for the base NETCONF Protocol [NETCONF]
are valid. It is assumed that the <partial-lock> and <partial-
unlock> RPCs are only allowed for an authenticated user after passing
some access control mechanism.
A lock either a partial-lock or a global lock might prevent other
users from configuring the system. The following mechanisms are in
place to prevent the misuse of this possibility:
Only an authenticated user after passing access control can
request a partial-lock.
The partial-lock is automatically released when a session is
terminated irrespective of the manner the session ends.
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The <kill-session> operation allows terminating other users
sessions.
The NETCONF server may log partial-lock requests in an audit
trail.
Partial locking is NOT an authorization mechanism, it should not be
used to provide security or access control. Partial locking should
only be used as a mechanism to provide consistency in case of
multiple managers trying to configure the node. It is vital that the
operator can easily understand the exact scope of a lock, for this
reason the scope is determined when granting a lock and is not
modified dynamically later.
4. 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 [NETCONF] section 10.3.
+---------------+---------------------------------------------------+
| Index | Capability Identifier |
+---------------+---------------------------------------------------+
| :partial-lock | urn:ietf:params:netconf:capability:partial-lock:1 |
| | .0 |
+---------------+---------------------------------------------------+
URI: urn:ietf:params:xml:ns:netconf:partial-lock:1.0
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
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5. Appendix A - XML Schema for Partial Locking (normative)
The following XML Schema defines the <partial-lock> and <partial-
unlock> operations:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:netconf:partial-lock:1.0"
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
targetNamespace="urn:ietf:params:xml:ns:netconf:partial-lock:1.0"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:annotation>
<xs:documentation>
Schema defining the partial-lock and unlock operations.
organization "IETF NETCONF Working Group"
contact
"Balazs Lengyel
Ericsson Hungary, Inc.
balazs.lengyel@ericsson.com"
</xs:documentation>
</xs:annotation>
<xs:import namespace="urn:ietf:params:xml:ns:netconf:base:1.0"
schemaLocation="netconf.xsd"/>
<xs:complexType name="partialLockType">
<xs:complexContent>
<xs:extension base="nc:rpcOperationType">
<xs:sequence>
<xs:element ref="nc:config-name"/>
<xs:element name="select" type="xs:string"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="partialUnLockType">
<xs:complexContent>
<xs:extension base="nc:rpcOperationType">
<xs:sequence>
<xs:element name="lock-id" type="xs:unsignedInt"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
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<!-- <partial-lock> operation -->
<xs:element name="partial-lock" type="partialLockType"
substitutionGroup="nc:rpcOperation"/>
<!-- <partial-unlock> operation -->
<xs:element name="partial-unlock" type="partialUnLockType"
substitutionGroup="nc:rpcOperation"/>
<!-- reply to <partial-lock> -->
<xs:element name="lock-id" type="xs:unsignedInt"/>
</xs:schema>
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6. Appendix B - YANG Module for Partial Locking (non-normative)
The following YANG module defines the <partial-lock> and <partial-
unlock> operations. The YANG language is defined in
[I-D.ietf-netmod-yang].
module netconf-partial-lock {
namespace urn:ietf:params:xml:ns:netconf:partial-lock:1.0;
prefix pl;
organization "IETF NETCONF Working Group";
contact
"Balazs Lengyel
Ericsson Hungary, Inc.
balazs.lengyel@ericsson.com";
description
"This YANG module defines the <partial-lock> and
<partial-unlock> operations.";
revision 2008-06-06 {
description "Initial version.";
}
grouping configName {
description
"A choice to list the datastore names for NETCONF.
This could be moved to a netconf.yang module.";
choice configNameType {
leaf running { type empty; }
leaf candidate { type empty; }
leaf startup { type empty; }
}
}
rpc partial-lock {
description "A NETCONF operation that locks part of a datastore.";
input {
uses configName;
leaf-list select {
description
"XPath expression that specifies the scope of the lock.
An Instance Identifier expression must be used unless the
:xpath capability is supported in which case any XPath 1.0
expression is allowed.";
type string;
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min-elements 1;
}
}
output {
leaf lockId {
description
"Identifies the lock, if granted. The lockId must be
used in the partial-unlock rpc.";
type uint32;
}
}
}
rpc partial-unlock {
input {
leaf lockId {
description
"Identifies the lock to be released. Must be the value
received in the response to the partial-lock operation.";
type uint32;
}
}
}
}
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7. Appendix C - Change Log
7.1. 01-02
Made XSD normative
Clarified that no specific access control is assumed.
Clarified that non-existing nodes are NOT covered by the lock, even
if they where existing and covered by the lock when it was originally
granted.
Some rewording
Added app-tags for two of the error cases.
Made YANG an informative reference
Enhanced security considerations.
7.2. 00-01
Added YANG module.
7.3. -00
Created from draft-lengyel-ngo-partial-lock-01.txt
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8. Acknowledgements
Thanks to Andy Bierman, Sharon Chisholm, Phil Shafer , David
Harrington, Mehmet Ersue and many other members of the NETCONF WG for
providing important input to this document.
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9. References
9.1. Normative References
[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.
9.2. Informative References
[I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for
NETCONF", draft-ietf-netmod-yang-00 (work in progress),
May 2008.
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Authors' Addresses
Balazs Lengyel
Ericsson Hungary
Email: balazs.lengyel@ericsson.com
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
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