NETCONF                                                       B. Lengyel
Internet-Draft                                                  Ericsson Hungary
Intended status: Standards Track                            M. Bjorklund
Expires: February 7, May 2, 2009                                      Tail-f Systems
                                                         August 06,
                                                        October 29, 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 RPCs, used to 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  Candidate Configuration Capability . . . . . . . . . . . . .  9
       2.6.2.  Candidate Configuration  Confirmed Commit Capability  . . . . . . . . . . . . .  9
       2.6.3.  Distinct Startup Capability  . . . . . . . . . . . . .  9 10
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9 10
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10 11
   5.  Appendix A  -  XML Schema for Partial Locking (normative)  . . 11 12
   6.  Appendix B  - YANG Module for Partial Locking
       (non-normative)  . . . . . . . . . . . . . . . . . . . . . . . 13 16
   7.  Appendix C  -  Change Log  . . . . . . . . . . . . . . . . . . 15 19
     7.1.  02-03  03-04  . . . . . . . . . . . . . . . . . . . . . . . . . . 15 19
     7.2.  01-02  02-03  . . . . . . . . . . . . . . . . . . . . . . . . . . 15 19
     7.3.  00-01  01-02  . . . . . . . . . . . . . . . . . . . . . . . . . . 15 19
     7.4.  00-01  . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     7.5.  -00  . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 20
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 21
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 22
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 17 22
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 17 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 23
   Intellectual Property and Copyright Statements . . . . . . . . . . 19 24

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 more limited scope smaller then than 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 begins when the partial lock is granted.  The partial lock
   granted and lasts until (1) either the corresponding <partial-unlock>
   operation succeeds or (2) the NETCONF session terminates.

   A NETCONF session MAY have multiple parts of one or more datastores
   (running, candidate,startup) 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.  If optionally  Optionally, if the :xpath
   capability is also supported, the device MUST also support the
   usage of using 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.
   one or more datastores.  The portion to lock is specified by using with XPath
   expressions in the select elements and the list of datastores in the
   target element in the <partial-lock> operation.  Each XPath
   expression MUST return a node set.  Locking a node also protects the
   complete subtree under it the node from modification by others.

   In some situations it is desirable that the same set of nodes are
   locked in more than one datastore.  As an example: if an interface is
   configured in the candidate datastore, it is dangerous if it is
   configured by someone else in a possibly conflicting manner in the
   running datastore.  For this reason <partial-lock> allows the locking
   of the same sections of the management data in one or multiple

   The select XPath expressions are evaluated only once at lock time,
   thereafter 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
   datastore(s) or none; I.e. none.  That is, if during the <partial-lock>
   operation one of the requested parts cannot be locked locked, the server
   MUST unlock all parts that have
   been already were previously locked during that

   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 no longer covered by the lock anymore. lock.  If all top
   level nodes are deleted, the lock will still be present, however
   it's present.  However,
   its scope will become nil i.e. it (i.e., the lock will not cover any nodes. nodes).

   A NETCONF server MUST be able to grant multiple simultaneous partial
   locks to a single NETCONF session.  If the scope of the individual
   locks overlaps, nodes in the common area MUST be locked until all of
   the locks are released.

   A partial lock operation MUST fail if:

   o  Any NETCONF session (including the current session) owns the
      global lock on the any target 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 control, and the locking user
      does not have sufficient privileges, rights to all parts of the a 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

   As with most locking systems, it 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 possible that two management
   sessions trying to lock different parts of the configuration could
   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 previously acquired locks, and
   retry the procedure after waiting some time interval.  The length of
   the interval should preferably SHOULD be random to avoid repeated dead-locks when both
   (or all) clients back down and then
   repeat locking.

   It is retry the intention to keep partial-locking simple, partial lock operation.

   The <partial-lock> operation is designed for simplicity, 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: addressed:

   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 (e.g.,
      changes depend on data values in the unlocked part of the datastore, the operator should include
      datastore), these values SHOULD be included in the scope of the

   o  An operator is allowed to edit the configuration  Configuration data can be edited both inside and outside the scope
      of a lock.  It is the operator's responsibility of the NETCONF client
      application to lock all relevant parts of the a 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 MUST fail even if the global lock is attempted requested by
   same NETCONF session which that owns the partial-lock. partial lock.  Parameters, Result, Examples


   target:  Name of the one or more configuration datastore datastores of which a part
       shall be locked.  One <partial-lock> operation can affect only one of  If multiple datastores are specified the
       datastores.  URLs same
       select parameter(s) are not accepted. used for all of them.  For each datastore
       locking of the same set of nodes will be requested.

   select:  One or more 'select' elements 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.

       Each select expression is evaluated for each targeted datastore.

       The nodes that matched the select expressions expression and are locked are
       reported in the rpc-reply message.  Note that if some of the
       requested nodes exist only in one of the datastores, the lock is
       granted on different nodes in different datastores.

       Each select expression MUST each return a node set, and at least one
       of the node sets must for one of the specified datastores MUST be non-empty. non-

       If the device supports the :xpath capability as well capability, any valid XPath 1.0
       expression can be used, if not, used.  If the device does not support the
       :xpath capability, 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

            <select xmlns:rte="">
            <select xmlns:if="">

          <locked-node xmlns:rte="">
          <locked-node xmlns:if="">

   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> <rpc-reply>
   element.  A list of locked nodes per datastore is also returned in
   Instance Identifier format.

   Negative Response:

   If a lock is already held by another session 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, session, a <session-id> of 0
   (zero) is included.  If needed the returned session-id may be used to
   <kill-session> the NETCONF session holding the lock.  The same error
   response is returned if the requesting session already holds the
   (global) lock for the same datastore.

   If all the select expressions return an empty node set, the <error-tag> <error-
   tag> is 'operation-failed', and the <error-app-tag> is 'no-matches'.

   If any select expression returns anything but something other than a node set, the <error-
   <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 cannot be used to lock non-existing non-existent nodes, which would
   reserving attempt to reserve them for future use.  To make sure guarantee
   that a node cannot be created by some other session, the parent node should
   SHOULD be locked, the top level node of the new section created, and
   then locked with another <partial-lock> operation.  After this this, the
   lock on the parent node should SHOULD be removed.

2.4.2.  <partial-unlock>

   The operation unlocks a part the parts of a datastore the datastores that was were
   previously locked using <partial-lock> during the same session.


   lock-id:  Lock identifier to unlock; unlock, taken from a reply to a previous
       <partial-lock> operation.

   Example: Unlock a previously created lock

      <nc:rpc xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0" xmlns="urn:ietf:params:xml:ns:netconf:partial-lock: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 parts of the datastore has datastore(s) have already been

   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 successful partial lock will cause another a subsequent operation to fail, fail
   if it
   tries attempts to modify the locked area and is executed in a NETCONF
   session other then than the one session that owns the lock.  Affected  All operations include:
   that modify the datastore are affected, including: <edit-config>,
   <copy-config>, <delete-config>, <commit> and <discard-
   changes>. <discard-changes>.  A granted partial-lock
   successful partial lock will also cause the (global) <lock> operation
   to fail.  All of these operations are affected only if they are for
   targeting 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  Partial locking of
   the candidate datastore does not depend on whether the datastore was
   modified or not.

2.6.2.  Confirmed Commit Capability


   o  a partial lock is requested for the running datastore, and

   o  the NETCONF server implements the :confirmed-commit capability,

   o  there was a recent confirmed <commit> operation where the
      confirming <commit> operation has not been received

   then 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.  The NETCONF server might therefore need to modify the
   In this case the <error-tag> 'in-use' and the <error-app-tag> 'Lock
   denied, Outstanding confirmed commit' is returned.

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 are relevant as for the base NETCONF Protocol [NETCONF]
   are valid.
   [NETCONF].  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 (either a partial-lock partial lock or a global lock 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 and authorized user after passing access control can request a partial-lock. partial

      The partial-lock partial lock is automatically released when a session is
      terminated irrespective regardless of the manner how the session ends.

      The <kill-session> operation allows terminating makes it possible to terminate other users
      users's sessions.

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

   A lock that is hung for some reason (e.g., a broken TCP connection
   that the server has not yet recognised) can be released using another
   NETCONF session by explicitly killing the session owning that lock
   using the <kill-session> operation.

   Partial locking is NOT an authorization mechanism, mechanism; it should not SHOULD NOT be
   used to provide security or access control.  Partial locking should SHOULD
   only be used as a mechanism to provide for providing consistency in case of when multiple
   managers are trying to configure the node.  It is vital that the
   operator can users
   easily understand the exact scope of a lock, for this
   reason lock.  This is why the scope
   is determined when granting a lock and is not modified dynamically later. thereafter.

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. one or more datastores.
        <xs:extension base="nc:rpcOperationType">
            <xs:element name="target">
                  A list of one or more datastore names for NETCONF.
       <xs:extension base="nc:rpcOperationType">
                  <xs:element ref="nc:config-name"/> name="startup" minOccurs="0">
                  <xs:element name="candidate" minOccurs="0">
                  <xs:element name="running" minOccurs="0">
            <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">
                  Identifies the lock to be released. Must lock, SHOULD be the value
                 received used in the response to the subsequent
                  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:complexType name="dataPartInPpartialLockReplyType">
          In a reply to a successful partial-lock request the content
          of the <rpc-reply> element MUST conform to this complex type.
        <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.
        <xs:element name="running" minOccurs="0">
              List of locked nodes in the running datastore.
              <xs:element name="locked-node" type="xs:string"
        <xs:element name="candidate" minOccurs="0">
              List of locked nodes in the candidate datastore.
              <xs:element name="locked-node" type="xs:string"
        <xs:element name="startup" minOccurs="0">
              List of locked nodes in the startup datastore.
              <xs:element name="locked-node" type="xs:string"


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 2008-10-31 {
     description "Initial version.";

   grouping configName configNames {
     container target {
             "A choice to list the of one or more datastore names for NETCONF.
         This could be moved to a netconf.yang module.";
      choice configNameType { names.";
         leaf running   { type empty; }
         leaf candidate { type empty; }
         leaf startup   { type empty; }
         must "running or candidate or startup" {
             error-message "At least one datastore must be specified.";

   rpc partial-lock {
       "A NETCONF operation that locks part of a datastore."; one or more datastores.";
     input {
       uses configName; configNames;
       leaf-list select {
           "XPath expression that specifies the scope of the lock.
           An Instance Identifier expression must MUST be used unless the
           :xpath capability is supported supported, in which case any XPath 1.0
           expression is allowed.";
         type string;
         min-elements 1;
     output {
       leaf lock-id {
           "Identifies the lock, if granted. The lock-id must MUST be
            used in the partial-unlock rpc.";
         type uint32;
       container running {
           leaf-list locked-node {
               description "List of locked nodes
                            in the running datastore";
               type instance-identifier;
       container candidate {
           leaf-list locked-node {
               description "List of locked nodes
                            in the candidate datastore";
               type instance-identifier;
       container startup {
           leaf-list locked-node {
               description "List of locked nodes
                            in the startup datastore";
               type instance-identifier;

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

7.  Appendix C  -  Change Log

7.1.  03-04

   Minor clarifications

   Added list of locked-nodes to the output of partial-lock.

   Added <target> wrapper around datastore names.

   Allowed atomic/one operation locking of datastore parts in multiple

   Improved English (hopefully)

   Removed the <data> element from rpc-reply following the text of

7.2.  02-03

   Minor clarifications

   Same descriptions in XSD and YANG.


7.3.  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.


7.4.  00-01

   Added YANG module.


7.5.  -00

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

8.  Acknowledgements

   Thanks to Andy Bierman, Sharon Chisholm, Phil Shafer , David
   Harrington, Mehmet Ersue Ersue, Wes Hardaker 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 draft-ietf-netmod-yang-01 (work in progress),
              August 2008.

Authors' Addresses

   Balazs Lengyel
   Ericsson Hungary


   Martin Bjorklund
   Tail-f Systems


Full Copyright Statement

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   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
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