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Versions: (draft-boutros-mpls-tp-li-lb) 00 01
02 03 04 05 06 07 08 RFC 6435
Network Working Group Sami Boutros (Ed.)
Internet Draft Siva Sivabalan (Ed.)
Intended status: Standards Track Cisco Systems, Inc.
Updates: 6371 (if approved)
Expires: March 29, 2012
Rahul Aggarwal (Ed.)
Arktan, Inc.
Martin Vigoureux (Ed.)
Alcatel-Lucent
Xuehui Dai (Ed.)
ZTE Corporation
September 29, 2011
MPLS Transport Profile lock Instruct and Loopback Functions
draft-ietf-mpls-tp-li-lb-06.txt
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Abstract
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This document specifies one function and describes a second function
which are applicable to MPLS transport networks. The first function
enables an operator to lock a transport path while the second enables
an operator to set, in loopback, a given node along a transport path.
This document also defines the extension to MPLS operation,
administration, and maintenance (OAM) to perform the lock function.
This document updates RFC 6371 section 7.1.1.
Table of Contents
1. Introduction...................................................2
1.1. Updates RFC 6371..........................................5
2. Terminology....................................................5
3. Lock Message...................................................5
3.1. Message Identification....................................5
3.2. LI Message Format.........................................6
4. Lock, Loopback and maintenance operations......................6
5. Operation......................................................7
5.1. Lock Operation............................................7
5.2. UnLock Operation..........................................7
5.3. General Procedures........................................7
5.4. Example Topology..........................................8
5.5. Locking a transport path..................................8
5.6. UnLocking a transport path................................8
6. Security Considerations........................................8
7. IANA Considerations............................................9
7.1. Pseudowire Associated Channel Type........................9
8. Acknowledgements...............................................9
9. References.....................................................9
9.1. Normative References......................................9
9.2. Informative References...................................10
Author's Addresses...............................................10
Full Copyright Statement.........................................12
Intellectual Property Statement..................................12
1. Introduction
This document specifies one function and describes another function
which are applicable to MPLS transport networks.
The first function enables an operator to lock a transport path. The
second function enables an operator to set that transport path in
loopback at a specified node along the path. This document also
specifies the extensions to the MPLS operation, administration and
maintenance (OAM) to perform the lock function.
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The Lock function pertains to Label Switched Paths (LSPs),
Pseudowires (including multi-segment Pseudowires) and Sections. As
per RFC 5860 [1], lock is an administrative state in which it is
expected that no client traffic may be carried. However, test traffic
and OAM messages can be mapped on the locked transport path.
Taking the example of an LSP, lock is initiated by an operator.
Typically when an LSP is locked, both ends of the LSP are
independently locked by the operator. It is often difficult to
coordinate these lock operations within a tight window. This document
defines a new OAM message, Lock Instruct (LI) in order to provide the
desired timely coordination.
When an endpoint of an LSP or PW is locked by an operator, the MEP
sends LI messages to its peer MEP. An endpoint considers the LSP to
be locked when either it receives an external operator command or
when it receives an LI message.
The Lock function can be performed using an extension to the MPLS OAM
as described in the next sections. This is a common mechanism to lock
PWs, LSPs and Sections.
The Lock function can as well be realized using a management plane.
The Loopback function is operated by management from MEP to MEP on
bidirectional (associated and co-routed) Label Switched Paths (LSPs),
Pseudowires (including multi-segment Pseudowires) and Sections.
The Loopback function is additionally operated from MEP to MIP on
co-routed bidirectional LSPs, on multi-segment Pseudowires and
Sections.
Loopback is a function that enables a receiving MEP to return
traffic to the sending MEP when in the loopback state. This state
corresponds to the situation where, at a given node, a forwarding
plane loop is configured and the incoming direction of a transport
path is cross-connected to the outgoing reverse direction. Therefore,
except in the case of early TTL expiry, traffic sent by the source
will be received by that source.
Note that before setting a given node in Loopback for a specific
transport path, this transport path MUST be locked.
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Data plane loopback is an out-of-service function, as required in
section 2.2.5 of RFC 5860 [1]. This function loops back all traffic
(including user data and OAM). The traffic can be originated from one
internal point at the ingress of a transport path within an interface
or inserted from input port of an interface using an external test
equipment. The traffic is looped back unmodified (other than normal
per hop processing such as TTL decrement) in the direction of the
point of origin by an interface at either an intermediate node or a
terminating node.
It should be noted that data plane loopback function itself is
applied to data plane loopback points residing on different
interfaces from MIPs/MEPs. All traffic (including both payload and
OAM) received on the looped back interface is sent on the reverse
direction of the transport path.
For data plane loopback at an intermediate point in a transport
path, the loopback needs to be configured to occur at either the
ingress or egress interface. This is done using management.
The Loopback can be performed using a management plane. Management
plane MUST ensure that the two MEPs are locked before performing the
loopback function.
The Lock function is based on a new G-ACH message using a new
channel type as well as an existing TLV.
When an LSP is locked, the management or control function is expected
to lock both ends. The purpose of the Lock instruct LI message is to
ensure the timely coordination of locking and unlocking the two ends.
Lock Instruct messages may be lost during looping or maintenance
operations, thus locking both ends is required, before such
operations occur.
This document updates RFC 6371 section 7.1.1.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [2].
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1.1. Updates RFC 6371
This document updates section 7.1.1 of RFC 6371. The mechanism
proposed to send the LI OAM message requires the LI OAM message to be
sent periodically and doesn't require a reply to the LI message.
2. Terminology
ACH: Associated Channel Header
LSR: Label Switching Router
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point.
MPLS-TP: MPLS Transport Profile
MPLS-OAM: MPLS Operations, Administration and Maintenance
MPLS-TP LSP: Bidirectional Label Switch Path
NMS: Network Management System
TLV: Type Length Value
TTL: Time To Live
LI: Lock Instruct
Transport path: MPLS-TP LSP or MPLS Pseudowire.
3. Lock Message
3.1. Message Identification
The proposed mechanism uses a new code point in the Associated
Channel Header (ACH) described in [4].
The LI channel is identified by the ACH as defined in RFC 5586 [4]
with the Channel Type set to the LI code point = 0xHH. [HH to be
assigned by IANA from the PW Associated Channel Type registry] The
LI Channel does not use ACH TLVs and MUST NOT include the ACH TLV
header. The LI ACH Channel is shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version|Reserved | 0xHH (LI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ACH Indication of LI
The LI Channel is 0xHH (to be assigned by IANA)
3.2. LI Message Format
The format of an LI Message is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Reserved | Refresh Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MEP Source ID TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS LI Message Format
Version: The Version Number is currently 1. (Note: the version
number is to be incremented whenever a change is made that affects
the ability of an implementation to correctly parse or process the
message. These changes include any syntactic or semantic changes made
to any of the fixed fields, or to any Type-Length-Value (TLV) or sub-
TLV assignment or format that is defined at a certain version number.
The version number may not need to be changed if an optional TLV or
sub-TLV is added.)
Refresh Timer: The maximum time between successive LI messages
specified in seconds. The default value is 1. The value 0 is not
permitted. When a lock is applied, a refresh timer is chosen. This
value MUST NOT be changed for the duration of that lock.
MEP Source ID TLV: This is the "CC/CV MEP ID TLV" defined in [3].
4. Lock, Loopback and maintenance operations
When an LSP is locked, the management or control function is expected
to lock both ends. The purpose of the LI message is to ensure the
timely coordination of locking and unlocking the two ends. LI
messages may be lost during looping or maintenance operations, thus
locking both ends is required, before such operations occur.
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When a transport path is put in loopback, traffic sent from the
sending MEP will be looped back to that sending MEP. OAM packets not
intercepted by TTL expiry will as well be looped back. The use of
traffic to measure packet loss, delay and delay variation is outside
the scope of this document.
5. Operation
5.1. Lock Operation
Lock is used to request a MEP to take a transport path out of service
for administrative reasons. For example, Lock can be used to allow
some form of maintenance to be done for a transport path.
When performing Lock, in response to a management request, the MEP
MUST take the transport path out of service and MUST begin sending LI
messages periodically to the remote MEP at the remote end of the
transport path.
The receiver MEP once locked, MUST take the transport path out of
service.
The receiver MEP, will lock the transport path as long as it is
receiving the periodic LI messages.
A MEP is locked either Lock was requested by management (and - as a
result it is sending LI messages), or it is receiving LI messages
from the remote MEP.
5.2. UnLock Operation
Unlock is used to request a MEP to bring the previously locked
transport path back in service.
When a MEP is unlocked via management or control it MUST cease
sending LI messages. Further, it must have stopped receiving LI
messages for a period of 3.5 times the previously received refresh
timer before it brings the transport path back in service.
A MEP would unlock transport path and put it back to service if and
only if there is no management request to lock the path and it is not
receiving in-band LI messages.
A MEP is unlocked when there is no management request to Lock and no
LI OAM messages are received.
5.3. General Procedures
When taking a transport path out of service, the operation MUST be
preceded by a lock operation.
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5.4. Example Topology
The next sections discuss the procedures for locking, Unlocking a
transport path. Assume a transport path traverses nodes A <--> B <--
> C <--> D. We will refer to the Maintenance Entities involved as
MEP-A, MIP-B, MIP-C, and MEP-D respectively. Suppose a maintenance
operation invoked at MEP-A requires to lock the transport path.
The following sections describe MEP-A setting and unsetting a lock at
MEP-D.
5.5. Locking a transport path
1. MEP-A sends an in-band LI Message in response to a management
request to lock the transport path. The message will include the
source MEP-ID TLV.
2. Upon receiving the LI message, D uses the received label stack and
the source MEP-ID as per [3] to identify the transport path. If no
label binding exists or there is no associated transport path back to
the originator, or if the source MEP-ID does not match, the event is
logged and processing of the LI message ceases.
5.6. UnLocking a transport path
1. In response to a management request to unlock the transport path
MEP-A stops sending LI Messages.
2. After both MEP A and MEP D have not received an LI message in at
least 3.5 times the refresh timer, and each MEP has not received a
new management request to Lock the transport path, both MEPs SHALL
put the transport path back in service.
6. Security Considerations
MPLS-TP is a subset of MPLS and so builds upon many of the aspects of
the security model of MPLS. MPLS networks make the assumption that it
is very hard to inject traffic into a network, and equally hard to
cause traffic to be directed outside the network. The control plane
protocols utilize hop-by-hop security, and assume a "chain-of-trust"
model such that end-to-end control plane security is not used. For
more information on the generic aspects of MPLS security, see [6].
This document describes a protocol carried in the G-ACh [4], and so
is dependent on the security of the G-ACh, itself. The G-ACh is a
generalization of the Associated Channel defined in [7]. Thus, this
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document relies heavily on the security mechanisms provided for the
Associated Channel and described in [4] and [7].
A specific concern for the G-ACh is that is can be used to provide a
covert channel. This problem is wider than the scope of this
document and does not need to be addressed here, but it should be
noted that the channel provides end-to-end connectivity and SHOULD
NOT be policed by transit nodes. Thus, there is no simple way of
preventing any traffic being carried between in the G-ACh consenting
nodes.
A good discussion of the data plane security of an associated channel
may be found in [5]. That document also describes some mitigation
techniques.
It should be noted that the G-ACh is essentially connection-oriented
so injection or modification of control messages specified in this
document require the subversion of a transit node. Such subversion is
generally considered hard in MPLS networks, and impossible to protect
against at the protocol level. Management level techniques are more
appropriate.
7. IANA Considerations
7.1. Pseudowire Associated Channel Type
LI OAM requires a unique Associated Channel Type which is assigned by
IANA from the Pseudowire Associated Channel Types Registry.
Registry:
Value Description TLV Follows Reference
----------- ----------------------- ----------- ---------
0xHH LI No (Section 3.1)
8. Acknowledgements
The authors would like to thank Loa Andersson, Yoshinori Koike,
D'Alessandro Alessandro Gerardo, Shahram Davari, Greg Mirsky, Yaacov
Weingarten, Liu Guoman, Matthew Bocci, Stewart Bryant and Adrian
Farrel for their valuable comments.
9. References
9.1. Normative References
[1] Vigoureux, M., Ward, D., and M. Betts, "Requirements for
Operations, Administration, and Maintenance (OAM) in MPLS
Transport Networks", RFC 5860, May 2010.
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[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] D. Allan, et. al., Proactive Connectivity Verification,
Continuity Check and Remote Defect indication for MPLS
Transport Profile draft-ietf-mpls-tp-cc-cv-rdi-06, work in
progress, June 2010
[4] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[5] T. Nadeau, C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, Dec 2007.
9.2. Informative References
[6] L. Fang, "Security Framework for MPLS and GMPLS Networks", RFC
5920, July 2010.
[7] S. Bryant, G. Swallow, L. Martini "Pseudowire Emulation Edge-
to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC
4385, Feb 2006.
Author's Addresses
Sami Boutros
Cisco Systems, Inc.
Email: sboutros@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
Email: msiva@cisco.com
Rahul Aggarwal
Arktan, Inc
EMail: raggarwa_1@yahoo.com
Martin Vigoureux
Alcatel-Lucent.
Email: martin.vigoureux@alcatel-lucent.com
Xuehui Dai
ZTE Corporation.
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Email: dai.xuehui@zte.com.cn
George Swallow
Cisco Systems, Inc.
Email: swallow@cisco.com
David Ward
Juniper Networks.
Email: dward@juniper.net
Stewart Bryant
Cisco Systems, Inc.
Email: stbryant@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@cisco.com
Eric Osborne
Cisco Systems, Inc.
Email: eosborne@cisco.com
Nabil Bitar
Verizon.
Email: nabil.bitar@verizon.com
Italo Busi
Alcatel-Lucent.
Email: italo.busi@alcatel-lucent.com
Lieven Levrau
Alcatel-Lucent.
Email: lieven.levrau@alcatel-lucent.com
Laurent Ciavaglia
Alcatel-Lucent.
Email: laurent.ciavaglia@alcatel-lucent.com
Bo Wu
ZTE Corporation.
Email: wu.bo@zte.com.cn
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Jian Yang
ZTE Corporation.
Email: yang_jian@zte.com.cn
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