Partial Lock Remote Procedure Call (RPC) for NETCONF :: RFC5717
Network Working Group B. Lengyel
Request for Comments: 5717 Ericsson
Category: Standards Track M. Bjorklund
Tail-f Systems
December 2009
Partial Lock Remote Procedure Call (RPC) for NETCONF
Abstract
The Network Configuration protocol (NETCONF) defines the lock and
unlock Remote Procedure Calls (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.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
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RFC 5717 Partial Lock RPC for NETCONF December 2009
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
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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
2.1.1. Usage Scenarios . . . . . . . . . . . . . . . . . . . 4
2.2. Dependencies . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Capability Identifier . . . . . . . . . . . . . . . . . . 5
2.4. New Operations . . . . . . . . . . . . . . . . . . . . . . 5
2.4.1. . . . . . . . . . . . . . . . . . . . . 5
2.4.2. . . . . . . . . . . . . . . . . . . . 10
2.5. Modifications to Existing Operations . . . . . . . . . . . 10
2.6. Interactions with Other Capabilities . . . . . . . . . . . 11
2.6.1. Candidate Configuration Capability . . . . . . . . . . 11
2.6.2. Confirmed Commit Capability . . . . . . . . . . . . . 11
2.6.3. Distinct Startup Capability . . . . . . . . . . . . . 11
3. Security Considerations . . . . . . . . . . . . . . . . . . . 12
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Normative References . . . . . . . . . . . . . . . . . . . 13
6.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. XML Schema for Partial Locking (Normative) . . . . . 14
Appendix B. YANG Module for Partial Locking (Non-Normative) . . . 17
Appendix C. Usage Example - Reserving Nodes for Future
Editing (Non-Normative) . . . . . . . . . . . . . . . 19
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1. Introduction
The [NETCONF] protocol describes the lock and unlock operations 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 a
capability-based extension to the NETCONF protocol to support partial
locking of the NETCONF running datastore using a mechanism based on
the existing XPath filtering mechanisms.
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].
Additionally, the following terms are defined:
o Instance Identifier: an XPath expression identifying a specific
node in the conceptual XML datastore. It contains an absolute
path expression in abbreviated syntax, where predicates are used
only to specify values for nodes defined as keys to distinguish
multiple instances.
o Scope of the lock: initially, the set of nodes returned by the
XPath expressions in a successful partial-lock operation. The set
might be modified if some of the nodes are deleted by the session
owning the lock.
o Protected area: the set of nodes that are protected from
modification by the lock. This set consists of nodes in the scope
of the lock and nodes in subtrees under them.
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 than a
complete configuration datastore. The scope to be locked is
specified by using restricted or full XPath expressions. Partial
locking only affects configuration data and only the running
datastore. The candidate or the start-up datastore are not affected.
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The system MUST ensure that configuration resources covered by the
lock are not modified by other NETCONF or non-NETCONF management
operations such as Simple Network Management Protocol (SNMP) and the
Command Line Interface (CLI).
The duration of the partial lock begins when the partial lock is
granted and lasts until (1) either the corresponding
operation succeeds or (2) the NETCONF session terminates.
A NETCONF session MAY have multiple parts of the running datastore
locked using partial lock operations.
The operation returns a lock-id to identify each
successfully acquired lock. The lock-id is unique at any given time
for a NETCONF server for all partial-locks granted to any NETCONF or
non-NETCONF sessions.
2.1.1. Usage Scenarios
In the following, we describe a few scenarios for partial locking.
Besides the two described here, there are many other usage scenarios
possible.
2.1.1.1. Multiple Managers Handling the Writable Running Datastore with
Overlapping Sections
Multiple managers are handling the same NETCONF agent simultaneously.
The agent is handled via the writable running datastore. Each
manager has his or her own task, which might involve the modification
of overlapping sections of the datastore.
After collecting and analyzing input and preparing the NETCONF
operations off-line, the manager locks the areas that are important
for his task using one single operation. The manager
executes a number of operations to modify the
configuration, then releases the partial-lock. The lock should be
held for the shortest possible time (e.g., seconds rather than
minutes). The manager should collect all human input before locking
anything. As each manager locks only a part of the data model,
usually multiple operators can execute the operations
simultaneously.
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2.1.1.2. Multiple Managers Handling the Writable Running Datastore,
Distinct Management Areas
Multiple managers are handling the same NETCONF agent simultaneously.
The agent is handled via the writable running datastore. The agent's
data model contains a number of well-defined separate areas that can
be configured without impacting other areas. An example can be a
server with multiple applications running on it, or a number of
network elements with a common NETCONF agent for management.
Each manager has his or her own task, which does not involve the
modification of overlapping sections of the datastore.
The manager locks his area with a operation, uses a
number of commands to modify it, and later releases the
lock. As each manager has his functional area assigned to him, and
he locks only that area, multiple managers can edit the configuration
simultaneously. Locks can be held for extended periods (e.g.,
minutes, hours), as this will not hinder other managers.
This scenario assumes that the global lock operation from [NETCONF]
is not used.
2.2. Dependencies
The device MUST support restricted XPath expressions in the select
element, as described in Section 2.4.1. Optionally, if the :xpath
capability is also supported (as defined in [NETCONF], Section 8.9.
"XPath Capability"), the device MUST also support using 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.
The operation allows the client to lock a portion of
the running datastore. The portion to lock is specified with XPath
expressions in the "select" elements in the operation.
Each XPath expression MUST return a node set.
When a NETCONF session holds a lock on a node, no other session or
non-NETCONF mechanism of the system can change that node or any node
in the hierarchy of nodes beneath it.
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Locking a node protects the node itself and the complete subtree
under the node from modification by others. The set of locked nodes
is called the scope of the lock, while all the locked nodes and the
nodes in the subtrees under them make up the protected area.
The XPath expressions are evaluated only once: at lock time.
Thereafter, the scope of the lock is maintained as a set of nodes,
i.e., the returned nodeset, and not by the XPath expression. If the
configuration data is later altered in a way that would make the
original XPath expressions evaluate to a different set of nodes, this
does not affect the scope of the partial lock.
Let's say the agent's data model includes a list of interface nodes.
If the XPath expression in the partial-lock operation covers all
interface nodes at locking, the scope of the lock will be maintained
as the list of interface nodes at the time when the lock was granted.
If someone later creates a new interface, this new interface will not
be included in the locked-nodes list created previously so the new
interface will not be locked.
A operation MUST be handled atomically by the NETCONF
server. The server either locks all requested parts of the datastore
or none. If during the operation one of the requested
parts cannot be locked, the server MUST unlock all parts that have
already been locked during that operation.
If a node in the scope of the lock is deleted by the session owning
the lock, it is removed from the scope of the lock, so any other
session or non-NETCONF mechanism can recreate it. If all nodes in
the scope of the lock are deleted, the lock will still be present.
However, its scope will become empty (since the lock will not cover
any nodes).
A NETCONF server that supports partial locking MUST be able to grant
multiple simultaneous partial locks to a single NETCONF session. If
the protected area of the individual locks overlap, nodes in the
common area MUST be protected until all of the overlapping locks are
released.
A operation MUST fail if:
o Any NETCONF session (including the current session) owns the
global lock on the running datastore.
o Any part of the area to be protected is already locked (or
protected by partial locking) by another management session,
including other NETCONF sessions using or any other
non-NETCONF management method.
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o The requesting user is not successfully authenticated.
o The NETCONF server implements access control and the locking user
does not have sufficient access rights. 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 operation.
The 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.
As a consequence, users must observe the following:
o Locking does not affect read operations.
o If part of the running datastore is locked, this has no effect on
any unlocked parts of the datastore. If this is a problem (e.g.,
changes depend on data values or nodes outside the protected part
of the datastore), these nodes SHOULD be included in the protected
area of the lock.
o Configuration data can be edited both inside and outside the
protected area of a lock. It is the responsibility of the NETCONF
client application to lock all relevant parts of the datastore
that are crucial for a specific management action.
Note: The operation does not modify the global
operation defined in the base NETCONF protocol [NETCONF]. If part of
the running datastore is already locked by , then a
global lock for the running datastore MUST fail even if the global
lock is requested by the NETCONF session that owns the partial lock.
2.4.1.1. Parameters, Results, Examples
Parameters:
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 nodes returned from the select expressions are reported in the
rpc-reply message.
Each select expression MUST return a node set, and at least one of
the node sets MUST be non-empty.
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If the device supports the :xpath capability, any valid XPath 1.0
expression can be 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
127
/rte:routing/rte:virtualRouter[rte:routerName='router1']
/if:interfaces/if:interface[if:id='eth1']
Note: The XML Schema in [NETCONF] has a known bug that requires the
XML element in a . This means that the above
examples will not validate using the XML Schema found in [NETCONF].
Positive Response:
If the device was able to satisfy the request, an is sent
with a element (lock identifier) in the
element. A list of locked nodes is also returned in Instance
Identifier format.
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Negative Response:
If any select expression is an invalid XPath expression, the is 'invalid-value'.
If any select expression returns something other than a node set, the
is 'invalid-value', and the is 'not-a-
node-set'.
If all the select expressions return an empty node set, the is 'operation-failed', and the is 'no-matches'.
If the :xpath capability is not supported and the XPath expression is
not an Instance Identifier, the is 'invalid-value', the
is 'invalid-lock-specification'.
If access control denies the partial lock, the is
'access-denied'. Access control SHOULD be checked before checking
for conflicting locks to avoid giving out information about other
sessions to an unauthorized client.
If a lock is already held by another session on any node within the
subtrees to be locked, the element is 'lock-denied' and
the element includes the of the lock owner.
If the lock is held by a non-NETCONF session, a of 0
(zero) SHOULD be included. The same error response is returned if
the requesting session already holds the (global) lock for the
running datastore.
If needed, the returned session-id may be used to the
NETCONF session holding the lock.
2.4.1.2. Deadlock Avoidance
As with most locking systems, it is possible that two management
sessions trying to lock different parts of the configuration could
become deadlocked. To avoid this situation, clients SHOULD lock
everything they need in one operation. If locking fails, the client
MUST back-off, release any previously acquired locks, and SHOULD
retry the procedure after waiting some randomized time interval.
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2.4.2.
The operation unlocks the parts of the running datastore that were
previously locked using during the same session. The
operation unlocks the parts that are covered by the lock identified
by the lock-id parameter. In case of multiple potentially
overlapping locks, only the lock identified by the lock-id is
removed.
Parameters:
lock-id: Identity of the lock to be unlocked. This lock-id MUST
have been received as a response to a lock request by the
manager during the current session, and MUST NOT have been
sent in a previous unlock request.
Example: Unlock a previously created lock
127
Positive Response:
If the device was able to satisfy the request, an is sent
that contains an element. A positive response MUST be sent even
if all of the locked parts of the datastore have already been
deleted.
Negative Response:
If the parameter does not identify a lock that is owned by
the session, an 'invalid-value' error is returned.
2.5. Modifications to Existing Operations
A successful partial lock will cause a subsequent operation to fail
if that operation attempts to modify nodes in the protected area of
the lock and is executed in a NETCONF session other than the session
that has been granted the lock. The 'in-use' and the
'locked' is returned. All operations that modify the
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running datastore are affected, including: , , , , and . If
partial lock prevents from modifying some data, but the
operation includes the continue-on-error option, modification of
other parts of the datastore, which are not protected by partial
locking, might still succeed.
If the datastore contains nodes locked by partial lock, this will
cause the (global) operation to fail. The element
'lock-denied' and an element including the
of the lock owner will be returned. If the lock is held by a non-
NETCONF session, a of 0 (zero) is returned.
All of these operations are affected only if they are targeting the
running datastore.
2.6. Interactions with Other Capabilities
2.6.1. Candidate Configuration Capability
The candidate datastore cannot be locked using the
operation.
2.6.2. Confirmed Commit Capability
If:
o a partial lock is requested for the running datastore, and
o the NETCONF server implements the :confirmed-commit capability,
and
o there was a recent confirmed operation where the
confirming 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
configuration.
In this case, the 'in-use' and the
'outstanding-confirmed-commit' is returned.
2.6.3. Distinct Startup Capability
The startup datastore cannot be locked using the
operation.
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3. Security Considerations
The same considerations are relevant as for the base NETCONF protocol
[NETCONF]. and RPCs MUST only be
allowed for an authenticated user. and RPCs SHOULD only be allowed for an authorized user. However,
as NETCONF access control is not standardized and not a mandatory
part of a NETCONF implementation, it is strongly recommended, but
OPTIONAL (although nearly all implementations include some kind of
access control).
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:
A user, that is not successfully authenticated, MUST NOT be
granted a partial lock.
Only an authorized user SHOULD be able to request a partial lock.
The partial lock is automatically released when a session is
terminated regardless of how the session ends.
The operation makes it possible to terminate other
users' sessions.
The NETCONF server MAY log partial lock requests in an audit
trail.
A lock that is hung for some reason (e.g., a broken TCP connection
that the server has not yet recognized) can be released using another
NETCONF session by explicitly killing the session owning that lock
using the operation.
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 for providing consistency when multiple
managers are trying to configure the node. It is vital that users
easily understand the exact scope of a lock. This is why the scope
is determined when granting a lock and is not modified thereafter.
4. IANA Considerations
This document registers one capability identifier URN from the
"Network Configuration Protocol (NETCONF) Capability URNs" registry,
and one URI for the NETCONF XML namespace in the "IETF XML registry"
[RFC3688]. Note that the capability URN is compliant to [NETCONF],
Section 10.3.
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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. Acknowledgements
Thanks to Andy Bierman, Sharon Chisholm, Phil Shafer, David
Harrington, Mehmet Ersue, Wes Hardaker, Juergen Schoenwaelder, Washam
Fan, and many other members of the NETCONF WG for providing important
input to this document.
6. References
6.1. 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.
6.2. Informative References
[YANG] Bjorklund, M., "YANG - A data modeling language for
NETCONF", Work in Progress, December 2009.
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RFC 5717 Partial Lock RPC for NETCONF December 2009
Appendix A. XML Schema for Partial Locking (Normative)
The following XML Schema defines the and operations:
Schema defining the partial-lock and unlock operations.
organization "IETF NETCONF Working Group"
contact
Netconf Working Group
Mailing list: netconf@ietf.org
Web: http://www.ietf.org/html.charters/netconf-charter.html
Balazs Lengyel
balazs.lengyel@ericsson.com
revision 2009-10-19
description Initial version, published as RFC 5717.
A number identifying a specific
partial-lock granted to a session.
It is allocated by the system, and SHOULD
be used in the unlock operation.
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A NETCONF operation that locks parts of
the running datastore.
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.
A NETCONF operation that releases a previously acquired
partial-lock.
Identifies the lock to be released. MUST
be the value received in the response to
the partial-lock operation.
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The content of the reply to a successful
partial-lock request MUST conform to this complex type.
Identifies the lock to be released. Must be the value
received in the response to a partial-lock operation.
List of locked nodes in the running datastore.
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Appendix B. YANG Module for Partial Locking (Non-Normative)
The following YANG module defines the and operations. The YANG language is defined in [YANG].
module ietf-netconf-partial-lock {
namespace urn:ietf:params:xml:ns:netconf:partial-lock:1.0;
prefix pl;
organization "IETF Network Configuration (netconf) Working Group";
contact
"Netconf Working Group
Mailing list: netconf@ietf.org
Web: http://www.ietf.org/html.charters/netconf-charter.html
Balazs Lengyel
Ericsson
balazs.lengyel@ericsson.com";
description
"This YANG module defines the and
operations.";
revision 2009-10-19 {
description
"Initial version, published as RFC 5717.";
}
typedef lock-id-type {
type uint32;
description
"A number identifying a specific partial-lock granted to a session.
It is allocated by the system, and SHOULD be used in the
partial-unlock operation.";
}
rpc partial-lock {
description
"A NETCONF operation that locks parts of the running datastore.";
input {
leaf-list select {
type string;
min-elements 1;
description
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"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.";
}
}
output {
leaf lock-id {
type lock-id-type;
description
"Identifies the lock, if granted. The lock-id SHOULD be
used in the partial-unlock rpc.";
}
leaf-list locked-node {
type instance-identifier;
min-elements 1;
description
"List of locked nodes in the running datastore";
}
}
}
rpc partial-unlock {
description
"A NETCONF operation that releases a previously acquired
partial-lock.";
input {
leaf lock-id {
type lock-id-type;
description
"Identifies the lock to be released. MUST be the value
received in the response to a partial-lock operation.";
}
}
}
}
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Appendix C. Usage Example - Reserving Nodes for Future Editing
(Non-Normative)
Partial lock cannot be used to lock non-existent nodes, which would
effectively attempt to reserve them for future use. To guarantee
that a node cannot be created by some other session, the parent node
should be locked, the top-level node of the new subtree created, and
then locked with another operation. After this, the
lock on the parent node should be removed.
In this section, an example illustrating the above is given.
We want to create Joe under , and start editing it.
Editing might take a number of minutes. We want to immediately lock
Joe so no one will touch it before we are finished with the editing.
We also want to minimize locking other parts of the running datastore
as multiple managers might be adding users near simultaneously.
First, we check what users are already defined.
Step 1 - Read existing users
The NETCONF server sends the following reply.
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Step 2 - Receiving existing data
fred8327
We want to add the new user Joe and immediately lock him using
partial locking. The way to do this, is to first lock all
nodes by locking the node.
Note that if we would lock all the nodes using the select
expression '/usr:top/usr:users/usr:user'; this would not lock the new
user Joe, which we will create after locking. So we rather have to
lock the node.
Step 3 - Lock users
The NETCONF server grants the partial lock. The scope of the lock
includes only the node. The lock protects the node
and all nodes below it from modification (by other sessions).
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Step 4 - Receive lock
1
/usr:top/usr:users
Next we create user Joe. Joe is protected by the lock received
above, as it is under the subtree rooted at the node.
Step 5 - Create user Joe
Joe
We receive a positive reply to the (not shown). Next
we request a lock, that locks only Joe, and release the lock
on the node. This will allow other managers to create
additional new users.
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Step 6 - Lock user Joe
The NETCONF server grants the partial lock. The scope of this second
lock includes only the node with name Joe. The lock protects
all data below this particular node.
Step 7 - Receive lock
2
/usr:top/usr:users/user[usr:name="Joe"]"
The scope of the second lock is the node Joe. It protects
this node and any data below it (e.g., phone number). At this
point of time, these nodes are protected both by the first and second
lock. Next, we unlock the other s and the node, to
allow other managers to work on them. We still keep the second lock,
so the node Joe and the subtree below is still protected.
Step 8 - Release lock on 1
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Authors' Addresses
Balazs Lengyel
Ericsson
EMail: balazs.lengyel@ericsson.com
Martin Bjorklund
Tail-f Systems
EMail: mbj@tail-f.com
Lengyel & Bjorklund Standards Track [Page 23]
