Network Working Group Sami Boutros (Ed.)
Internet Draft Siva Sivabalan (Ed.)
Intended status: Standards Track Cisco Systems, Inc.
Updates: 6371 (if approved)
Expires: April 3, 2012 Rahul Aggarwal (Ed.)
Arktan, Inc.
Martin Vigoureux (Ed.)
Alcatel-Lucent
Xuehui Dai (Ed.)
ZTE Corporation
October 3, 2011
MPLS Transport Profile lock Instruct and Loopback Functions
draft-ietf-mpls-tp-li-lb-07.txt
Abstract
Two useful Operations, Administration, and Maintenance (OAM)
functions in a transport network are "lock" and "loopback". The lock
function enables an operator to lock a transport path such that it
does not carry client traffic, but can continue to carry OAM messages
and may carry test traffic. The loopback function allows an operator
to set a specific node on the transport path into loopback mode such
that it returns all received data.
This document specifies the lock function for MPLS networks and
describes how the loopback function operates in MPLS networks.
This document updates RFC 6371 section 7.1.1.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
Two useful Operations, Administration, and Maintenance (OAM)
functions in a transport network are "lock" and "loopback". This
document discusses these functions in the context of MPLS networks.
- The lock function enables an operator to lock a transport path such
that it does not carry client traffic. 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
still be mapped onto the locked transport path. The lock function
may be applied to to Label Switched Paths (LSPs), Pseudowires (PWs)
(including multi-segment Pseudowires) (MS-PWs), and MPLS Sections
as defined in RFC 5960 [9]).
- The loopback function allows an operator to set a specific node on
a transport path into loopback mode such that it returns all
received data. Loopback can be applied at a Maintenance Entity
Group End Point (MEP) or a Maintenance Entity Group Intermediate
Point (MIP) on a co-routed bidirectional LSP, PW or MPLS
Section. It can also be applied at a MEP on an associated
bidirectional LSP, PW or MPLS Section.
Loopback is used to test the integrity of the transport path to and
from the node that is performing loopback. It requires that the
transport is locked and that a MEP on the transport path sends test
data which it also validates on receipt.
This document specifies the lock function for MPLS networks and
describes how the loopback function operates in MPLS networks.
This document updates RFC 6371 section 7.1.1 [6].
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1.1. Updates RFC 6371
This document updates section 7.1.1 of RFC 6371 [6].
That framework makes the assumption that the Lock Instruct message is
used to independently enable locking and requires a response message.
The mechanism defined in this document requires that a lock
instruction is sent by management to both ends of the locked
transport path and that the Lock Instruct message does not require a
response.
2. Terminology and Conventions
2.1. 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].
2.2. Acronyms and Terms
ACH: Associated Channel Header
MEG: Maintenance Entity Group
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point
MPLS-TP: MPLS Transport Profile
MPLS-TP LSP: Bidirectional Label Switch Path
TLV: Type Length Value
TTL: Time To Live
LI: Lock Instruct
Transport path: MPLS-TP LSP or MPLS PW
3. Lock Function
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. Lock is
also a prerequisite of the Loopback function described in Section 4.
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The NMS or a management process initiates a Lock by sending a Lock
command to a MEP. The MEP takes the transport path out of service,
that is, it stops injecting or forwarding traffic onto the transport
path.
To properly lock a transport path (for example, to ensure that a
loopback test can be performed), both directions of the transport
path must be taken out of service so a Lock command is sent to the
MEPs at both ends of the path. This ensures that no traffic is sent
in either direction. Thus, the Lock function can be realized entirely
using the management plane.
However, despatch of messages in the management plane to the two MEPs
may present coordination challenges. It is desirable that the lock be
achieved in a coordinated way within a tight window, and this may be
difficult with a busy management plane. In order to provide
additional coordination, an LI OAM message can additionally be sent.
A MEP locks a transport path when it receives a command from a
management process or when it receives an LI message as described in
Section 6.
This document defines an LI message for MPLS OAM. The LI message is
based on a new ACH Type as well as an existing TLV. This is a common
mechanism applicable to lock LSPs, PW, and MPLS Sections.
4. Loopback Function
This section provides a description of the Loopback function within
an MPLS network. This function is achieved through management
commands and so there is no protocol specification necessary.
However, the Loopback function is dependent on the Lock function and
so it is appropriate to describe it in this document.
The Loopback function is used to test the integrity of a transport
path from a MEP up any other node in the same MEG. This is achieved
by setting the target node into loopback mode, and transmitting a
pattern of test data from the MEP. The target node loops all received
data back toward the originator, and the MEP extracts the test data
and compares it with what it sent.
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.
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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 nature of test data and the use of loopback traffic to measure
packet loss, delay, and delay variation is outside the scope of this
document.
4.1. Operational Prerequisites
Obviously, for the Loopback function to operate, there are several
prerequisites:
- There must be a return path, so transport path under test must e
bidirectional.
- The node in loopback mode must be on both the forward and return
paths. This possible for all MEPs and MIPs on a co-routed
bidirectional LSP, PW, or MPLS Section, but is only
possible on for MEPs on associated bidirectional LSPs, PW,
or MPLS Sections.
- The transport path cannot deliver client data when one of its nodes
is in loopback mode, so it is important that the transport path is
locked before loopback is enabled.
- Management plane coordination between the node in loopback mode and
the MEP sending test data is required. The MEP must not send test
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data until loopback has been properly configured because this would
result in the test data continuing toward the destination.
- The TTL of the test packets must be set sufficiently large to
account for both directions of the transport path under test
otherwise the packets will not be returned to the originating MEP.
- OAM messages intended for delivery to nodes along the transport
path under test can be delivered by correct TTL expiry. However,
OAM messages cannot be delivered to points beyond the loopback node
until the loopback condition is lifted.
5. Lock Instruct Message
5.1. Message Identification
The Lock Instruct Message is carried in the Associated Channel Header
(ACh) described in [4]. it is identified by a new PW ACh Type of 0xHH
(to be assigned by IANA).
5.2. 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 1: MPLS Lock Instruct 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.)
Reserved: The reserved field MUST be set to zero on transmission and
SHOULD be ignored on receipt.
Refresh Timer: The maximum time between successive LI messages
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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. A node
receiving a LI message with a changed refresh timer MAY ignore the
new value and continue to apply the old value.
MEP Source ID TLV: This is one of the three MEP Source ID TLVs
defined in [3] and identifies the MEP that originated the LI message.
6. Operation of the Lock Function
6.1. Locking a Transport Path
When a MEP receives a Lock command from an NMS or through some other
management process, it MUST take the transport path out of service.
That is, it MUST stop injecting or forwarding traffic onto the LSP,
PW, or Section that has been locked.
As soon as the transport path has been locked, the MEP MUST send an
LI message targeting the MEP at the other end of the locked transport
path. The source MEP MUST set the Refresh Timer value in the LI
message and MUST retransmit the LI message at the frequency indicated
by the value set.
When locking a transport path, the NMS or management process is
required to send a Lock command to both ends of the transport path.
Thus a MEP may receive either the management command or an LI message
first. A MEP MUST take the transport path out of service immediately
in either case, but only sends LI messages itself after it has
received a management lock command. Thus, a MEP is locked if either
Lock was requested by management (and, as a result, the MEP is
sending LI messages), or it is receiving LI messages from the remote
MEP.
Note that a MEP that receives an LI message MUST identify the correct
transport path and validate the message. The label stack on the
received message is used to identify the transport path to be locked:
- If no matching label binding exists then there is no corresponding
transport path and the received LI message is in error.
- If the transport path can be identified, but there is no return
path (for example, the transport path was unidirectional) then the
lock cannot be applied by the receiving MEP.
- If the transport path is suitable for locking but the source MEP-ID
identifies an unexpected MEP for the MEG to which the receiving MEP
belongs, the received LI message is in error.
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When an errored LI message is received, the receiving MEP MUST NOT
apply a lock. A MEP receiving errored LI messages SHOULD perform
local diagnostic actions (such as counting the messages) and MAY
log the messages.
A MEP keeps a transport path locked as long as it is either receiving
the periodic LI messages or has an in-force Lock command from
management. (see Section 6.2 for an explanation of unlocking a MEP).
Note that in some scenarios (such as the use of loopback as described
in Section 4) LI messages will not continue to be delivered on a
locked transport path. This is why a transport path is considered
locked while there is an in-force Lock command from a management
process regardless of whether LI messages are being received.
6.2. UnLocking a Transport Path
Unlock is used to request a MEP to bring the previously locked
transport path back in service.
When a MEP receives an Unlocked command from a management process it
MUST cease sending LI messages. However, as described in Section 6.1,
if the MEP is still receiving LI messages, the transport path MUST
remain out of service. Thus, to unlock a transport path, the
management process has to send an Unlock command to the MEPs at
either end.
When a MEP has been unlocked and has not received an LI message for a
multiple of 3.5 times the Refresh Timer on the LI message (or has
never received an LI message), the MEP unlocks the transport path and
puts it back into service.
7. 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. For more
information on the generic aspects of MPLS security, see [7].
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 [8]. Thus, this
document relies heavily on the security mechanisms provided for the
Associated Channel and described in [4] and [8].
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
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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 in the G-ACh between 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.
8. IANA Considerations
8.1. 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 [This.I-D]
9. Acknowledgements
The authors would like to thank Loa Andersson, Yoshinori Koike,
Alessandro D'Alessandro Gerardo, Shahram Davari, Greg Mirsky, Yaacov
Weingarten, Liu Guoman, Matthew Bocci, and Adrian Farrel for their
valuable comments.
10. References
10.1. 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.
[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
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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.
[6] Busi, I. and Allan, D., "Operations, Administration, and
Maintenance Framework for MPLS-Based Transport Networks",
RFC 6371, September 2011
10.2. Informative References
[7] L. Fang, "Security Framework for MPLS and GMPLS Networks", RFC
5920, July 2010.
[8] S. Bryant, G. Swallow, L. Martini "Pseudowire Emulation Edge-
to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC
4385, Feb 2006.
[9] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS
Transport Profile Data Plane Architecture", RFC 5960, August
2010.
Editors' 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.
Email: dai.xuehui@zte.com.cn
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Contributing Authors
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
Jian Yang
ZTE Corporation.
Email: yang_jian@zte.com.cn
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