NETCONF B. Lengyel
Internet-Draft Ericsson Hungary
Intended status: Standards Track M. Bjorklund
Expires: August 28, 2008 Tail-f Systems
February 25, 2008
Partial Lock RPC for NETCONF
draft-ietf-netconf-partial-lock-01
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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> . . . . . . . . . . . . . . . . . . . 7
2.5. Modifications to Existing Operations . . . . . . . . . . . 8
2.6. Interactions with Other Capabilities . . . . . . . . . . . 8
2.6.1. Writable-Running Capability . . . . . . . . . . . . . 8
2.6.2. Candidate Configuration Capability . . . . . . . . . . 8
2.6.3. Distinct Startup Capability . . . . . . . . . . . . . 8
3. Security Considerations . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Appendix A - Change Log . . . . . . . . . . . . . . . . . . 10
5.1. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. 00-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Appendix B - YANG Module for Partial Locking
(non-normative) . . . . . . . . . . . . . . . . . . . . . . . 11
7. Appendix C - XML Schema for Partial Locking
(non-normative) . . . . . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
9. Normative References . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
The NETCONF protocol [RFC4741] 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 ensures that configuration resources covered by the lock
are not be 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
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
Partial locking uses only restricted XPath expressions to describe
the lock's scope, as described in Section 2.4.1 for the select
element. However if optionally the :xpath capability is also
supported, partial locking can utilize any Xpath 1.0 expression.
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 nodeset
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.
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.
A partial lock MUST fail if:
o Any NETCONF session (including the current session) owns the
global lock on the datastore.
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
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method.
o The NETCONF server implements access control and the locking user
does not have at least some basic access rights, e.g., read
rights, to all 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.
As with most locking systems, there is a possibility that two users
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 effect 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.
Note: The <partial-lock> operation does not modify the global <lock>
operation defined in the base NETCONF Protocol [RFC4741]. 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:
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target: Name of the configuration datastore of which a part shall be
locked. 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 return a node set.
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 [Editor's
Note: add text or reference]. 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.]
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/['interfaceId=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:
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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 shall be 'lock-denied' and the
<error-info> element shall include 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>
shall be 'operation-failed', and the <error-app-tag> shall be 'no-
matches'.
If any select expression returns anything but a node set, the <error-
tag> shall be 'invalid-value'.
If the :xpath capability is not supported and the XPath expression is
not an Instance Identifier, the <error-tag> shall be 'invalid-value'.
If access control denies the partial lock, the <error-tag> shall be
'access-denied'.
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:
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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.
2.5. Modifications to Existing Operations
None.
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 [RFC4741]
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.
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4. IANA Considerations
This document registers a URN for the the following NETCONF
capability in the netconf registry (RFC4741], sect 10.3):
+---------------+---------------------------------------------------+
| Index | Capability Identifier |
+---------------+---------------------------------------------------+
| :partial-lock | urn:ietf:params:netconf:capability:partial-lock:1 |
| | .0 |
+---------------+---------------------------------------------------+
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5. Appendix A - Change Log
5.1. Open Issues
Shall we allow the locking of non-existent nodes? The operator
might want to reserve an object or rather its key/name even if he
will create the object later.
Should we include more detailed information in error results to
help debug lock conflicts, e.g. the userId of the conflicting
session, the XPath expression of the conflicting session, the
instanceId of the first object where the lock conflict was found?
Should we allow users to lock parts of multiple datastores (e.g.
/top/routing both in the candidate and the running datastore) in
one operation? This would decrease the probability of a dead-
lock, but currently the (global) <lock> operation doesn't support
this.
5.2. -00
Created from draft-lengyel-ngo-partial-lock-01.txt
5.3. 00-01
Added YANG module.
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6. Appendix B - YANG Module for Partial Locking (non-normative)
The following Yang modul defines the <partial-lock> and <partial-
unlock> operations.
This and the following Appendix are non-normative as the method to
define NETCONF operations is not yet agreed. Either the YANG or the
XSD or some other model will later probably become normative.
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 2008-01-07 {
description "Inital 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 {
input {
uses configName;
leaf-list select {
type string;
min-elements 1;
}
}
output {
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leaf lockId { type uint32; }
}
}
rpc partial-unlock {
input {
leaf lockId { type uint32; }
}
}
}
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7. Appendix C - XML Schema for Partial Locking (non-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.
</xs:documentation>
</xs:annotation>
<xs:import namespace="urn:ietf:params:xml:ns:netconf:base:1.0"
schemaLocation="urn:ietf:params:xml:ns:netconf:base:1.0"/>
<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>
<!-- <partial-lock> operation -->
<xs:element name="partial-lock" type="partialLockType"
substitutionGroup="nc:rpcOperation"/>
<!-- <partial-unlock> operation -->
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<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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8. Acknowledgements
Thanks to Andy Bierman, Sharon Chisholm, Phil Shafer and many other
members of the NETCONF WG for providing important input to this
document.
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9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4741] "NETCONF Configuration Protocol", RFC 4741, December 2006.
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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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