NETCONF                                                       B. Lengyel
Internet-Draft                                          Ericsson Hungary
Intended status: Standards Track                            M. Bjorklund
Expires: December 15, 2008 February 7, 2009                                 Tail-f Systems
                                                           June 13,
                                                         August 06, 2008

                      Partial Lock RPC for NETCONF

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


   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.

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  02-03  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.2.  00-01  01-02  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.3.  00-01  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.4.  -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

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",
   "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 granted.  The partial lock lasts 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.

2.2.  Dependencies

   The device MUST support the restricted XPath expressions in the
   select element, as described in Section 2.4.1 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


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.  Locking a node
   protects the complete subtree under it from modification by others.

   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 operation 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

   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.

   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, Result, Examples


   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.

   Example: Lock virtual router 1 and interface eth1



   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
   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'.  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.


   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"

   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.

2.5.  Modifications to Existing Operations

   A granted partial-lock will cause operations that want another operation to fail, if it
   tries to modify the locked area to fail, if and is 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>. <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.

      The <kill-session> operation allows terminating other users

      The NETCONF server may log partial-lock requests in an audit

   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.

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=""
   elementFormDefault="qualified" attributeFormDefault="unqualified">

         Schema defining the partial-lock and unlock operations.
         organization "IETF NETCONF Working Group"
             "Balazs Lengyel
              Ericsson Hungary, Inc.

   <xs:import namespace="urn:ietf:params:xml:ns:netconf:base:1.0"

   <xs:complexType name="partialLockType">
         A NETCONF operation that locks part of a datastore.
       <xs:extension base="nc:rpcOperationType">
           <xs:element ref="nc:config-name"/>
           <xs:element name="select" type="xs:string"
                 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.

   <xs:complexType name="partialUnLockType">
         A NETCONF operation that releases a previously acquired
       <xs:extension base="nc:rpcOperationType">
           <xs:element name="lock-id" type="xs:unsignedInt"/> type="xs:unsignedInt">
                 Identifies the lock to be released. Must be the value
                 received in the response to the partial-lock operation.

   <!-- <partial-lock> operation -->
   <xs:element name="partial-lock" type="partialLockType"

   <!-- <partial-unlock> operation -->
   <xs:element name="partial-unlock" type="partialUnLockType"

   <!-- reply to <partial-lock> -->
   <xs:element name="lock-id" type="xs:unsignedInt"/>


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

  module netconf-partial-lock {

    namespace urn:ietf:params:xml:ns:netconf:partial-lock:1.0;
    prefix pl;

    organization "IETF NETCONF Working Group";

      "Balazs Lengyel
       Ericsson Hungary, Inc.";

      "This YANG module defines the <partial-lock> and
       <partial-unlock> operations.";

    revision 2008-06-06 {
      description "Initial version.";

    grouping configName {
        "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 {
            "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;
          min-elements 1;
      output {
        leaf lockId lock-id {
            "Identifies the lock, if granted. The lockId lock-id must be
             used in the partial-unlock rpc.";
          type uint32;

    rpc partial-unlock {
        "A NETCONF operation that releases a previously acquired
      input {
        leaf lockId lock-id {
            "Identifies the lock to be released. Must be the value
            received in the response to the partial-lock operation.";
          type uint32;

7.  Appendix C  -  Change Log

7.1.  02-03

   Minor clarifications

   Same descriptions in XSD and YANG.

7.2.  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

   Some rewording

   Added app-tags for two of the error cases.

   Made YANG an informative reference

   Enhanced security considerations.


7.3.  00-01

   Added YANG module.


7.4.  -00

   Created from draft-lengyel-ngo-partial-lock-01.txt

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.

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

              Bjorklund, M., "YANG - A data modeling language for
              NETCONF", draft-ietf-netmod-yang-00 (work in progress),
              May 2008.

Authors' Addresses

   Balazs Lengyel
   Ericsson Hungary


   Martin Bjorklund
   Tail-f Systems


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