Network Working Group M.Bocci, (Ed.)
Internet Draft Alcatel-Lucent
D.Ward, (Ed.)
Cisco
Intended status: Proposed Standard June 26, 2008
Expires: December 2008
MPLS Generic Associated Channel
draft-bocci-pwe3-mpls-tp-ge-ach-00.txt
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Copyright Notice
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Copyright (C) The IETF Trust (2008).
Abstract
This draft describes a generic associated channel header (GE-ACH)
that provides a control channel associated with an MPLS LSP,
pseudowire or MPLS section. The VCCV ACH defined for PWs in RFC 5085
is generalized to allow a larger set of control channel and OAM
functions to be used to meet the requirements of packet transport and
other applications of MPLS.
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 [1].
Table of Contents
1. Introduction................................................2
1.1. Contributing Authors....................................3
1.2. Objectives.............................................3
1.3. Scope..................................................3
1.4. Terminology............................................4
2. Generic Associated Channel...................................4
2.1. Generic Associated Channel Header.......................4
3. Congestion Considerations....................................5
4. Security Considerations......................................5
5. IANA Considerations.........................................5
6. Acknowledgments.............................................6
7. References..................................................6
7.1. Normative References....................................6
7.2. Informative References..................................7
Author's Addresses.............................................7
Intellectual Property Statement.................................8
1. Introduction
There is a need for Operations and Maintenance (OAM) mechanisms that
can be used for edge-to-edge (i.e. between originating and
terminating LSRs or T-PEs) and segment fault detection (e.g. between
any two LSRs or S-PEs along the path of an LSP or PW), diagnostics,
maintenance and other functions for a Pseudowire and an LSP. Some of
these functions can be supported using tools such as VCCV [3], BFD
[8], or LSP-Ping [7]. However, a requirement has been indicated to
extend these toolsets, in particular where MPLS networks are used for
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packet transport services and network operations [6]. These include
performance monitoring, automatic protection switching, and support
for management and signaling communication channels. These tools must
be applicable to, and function in essentially the same manner (from
an operational point of view) on both MPLS PWs and MPLS LSPs. They
must also operate in-band on the PW or LSP such that they do not
depend on PSN routing, user data traffic or ultimately on control
plane functions.
Virtual Circuit Connectivity Verification (VCCV) can use an
associated channel to provide a control channel between a PW's
ingress and egress points over which OAM and other control messages
can be exchanged. In this draft, we propose a generic associated
channel header (GE-ACH) to enable the same control channel mechanism
be used for MPLS Sections, LSPs and PWs. The associated channel
header (ACH) specified in RFC 4385 [2] is used with additional code
points to support additional MPLS OAM functions.
1.1. Contributing Authors
The editors gratefully acknowledge the following additional
contributors: Stewart Bryant, Italo Busi, Marc Lasserre, Lieven
Levrau, and Martin Vigoureux.
1.2. Objectives
This draft proposes a mechanism to provide for the OAM needs of
transport applications. It creates a generic OAM identification
mechanism that may be applied to all MPLS LSPs, while maintaining
compatibility with the PW associated channel header (ACH) [2]. It
also normalizes the use of the ACH for PWs in a transport context.
1.3. Scope
This draft defines the encapsulation header for LSP, MPLS Section and
PW associated channel messages.
It does not define how associated channel capabilities are signaled
or negotiated between LSRs or PEs, the operation of various OAM
functions, or the messages transmitted on the associated channel.
This draft does not deprecate existing MPLS and PW OAM mechanisms.
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1.4. Terminology
ACH: Associated Channel Header
MPLS Section: A Section is a network segment between two LSRs that
are immediately adjacent.
2. Generic Associated Channel
VCCV [3] defines three control channel types that may be used to
multiplex OAM messages onto a PW. CC type 1, uses an associated
channel header and is referred to as "In-band VCCV", CC type 2 which
uses the router alert label to indicate VCCV packets and is referred
to as "Out of Band VCCV", and CC type 3 that uses the TTL to force
the packet to be processed by the destination routers control plane
(known as "MPLS PW Label with TTL == 1").
This draft proposes that in transport applications only the type 1
(associated channel header) mechanism is used for LSP OAM and for PW
OAM. In transport applications a static or traffic engineered LSP is
normally used, thus the data and the OAM will follow the same path.
This does not preclude the use of the GE-ACH mechanism described in
this draft for other applications of MPLS.
Note that VCCV also includes mechanisms for negotiating the control
channel and connectivity verification (i.e. OAM tool) types between
PEs. These mechanisms need to be extended when a generic associated
channel is used for MPLS LSP OAM. This will most likely require
extensions to label distribution protocols and is outside the scope
of this document.
This section defines a generic associated channel header (GE-ACH)
that identifies packets on the associated channel.
2.1. Generic Associated Channel Header
The format of the GE-ACH for LSP, Section and PW associated channel
traffic is shown in Figure 1:
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 | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Generic Associated Channel Header
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The first nibble is set to 0001b to indicate a channel associated
with a PW or LSP. The Version and Reserved fields are set to 0, as
specified in RFC 4385 [2].
Values for the channel type used for VCCV are specified in RFC 4446
[4].
This draft specifies the following additional channel types:
0xXX - for OAM functions
0xYY - for APS functions
0xKK - for Management Communications Channel (MCC) functions
0xZZ - for Signaling Communications Channel (SCC) functions
The functionality of these channel types will be defined elsewhere.
3. Congestion Considerations
The congestion considerations detailed in RFC 5085 [1] apply. Further
generic associated channel-specific congestion considerations will be
detailed in a future revision of this draft.
4. Security Considerations
The security considerations detailed in RFC 5085 [1] apply. Further
generic associated channel-specific security considerations will be
detailed in a future revision of this draft.
5. IANA Considerations
This draft requests that code points for the following GE-ACH channel
types be allocated from the IANA PW Associated Channel Type registry
[4]:
0xXX - for OAM functions
0xYY - for APS functions
0xKK - for Management Communications Channel (MCC) functions
0xZZ - for Signaling Communications Channel (SCC) functions
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The PW Associated Channel Type registry is currently allocated based
on the IETF consensus process, described in [5]. This allocation
process was chosen based on the consensus reached in the PWE3 working
group that pseudowire associated channel mechanisms should be
reviewed by the IETF and only those that are consistent with the PWE3
architecture and requirements should be allocated a code point.
However, a requirement has emerged to allow for vendor-specific
optimizations or extensions to OAM and other control protocols
running in an associated channel, by supporting vendor specific code
points [6]. This would prevent code points used for such functions
from being allocated through the IETF standards process in future.
Vendor specific code point space thus protects an installed base of
equipment from potential inadvertent overloading of code points.
Each draft specifying ACH protocols must provide a solution for
supporting vendor-specific types, in accordance with [6], in addition
to those allocated by IETF consensus. The details of these solutions
are outside the scope of this draft.
6. Acknowledgments
The authors gratefully acknowledge the input of Lou Berger, George
Swallow and Rahul Aggarwal.
7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] S. Bryant et al., "Pseudowire Emulation Edge-to-Edge (PWE3)
Control Word for Use over an MPLS PSN", RFC 4385, February 2006
[3] Nadeau, T. & Pignataro, S., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", RFC 4446, April 2006
[5] Narten, T., Alvestrand, H., " Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998
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7.2. Informative References
[6] M. Vigoureux et al., "Requirements for OAM in MPLS Transport
Networks", draft-vigoureux-mpls-tp-oam-requirements-00.txt,
June 2008
[7] K. Kompella, G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006
[8] R. Aggarwal et al, "BFD for MPLS LSPs", draft-ietf-bfd-mpls-
07.txt, June 2008
Author's Addresses
Matthew Bocci, (Ed.)
Alcatel-Lucent
Voyager Place,
Maidenhead,
Berks, UK
Phone: +44 1633 413600
Email: matthew.bocci@alcatel-lucent.co.uk
David Ward, (Ed.)
Cisco
170 W. Tasman Dr.
San Jose, CA 95134 USA
Phone: +1-408-526-4000
Email: dward@cisco.com
Stewart Bryant
Cisco
250, Longwater,
Green Park,
Reading, RG2 6GB,
United Kingdom.
Email: stbryant@cisco.com
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Italo Busi,
Alcatel-Lucent
VIA TRENTO 30,
20059 VIMERCATE ITALY
Email: italo.busi@alcatel-lucent.it
Marc Lasserre
Alcatel-Lucent
16 Avenue Descartes,
92352 LE PLESSIS ROBINSON CEDE,
France
Email: mlaserre@alcatel-lucent.com
Lieven Levrau
Alcatel-Lucent
7-9, Avenue Morane,
Saulnier BP 57 78141,
VELIZY,
France
Email: llevrau@alcatel-lucent.com
Martin Vigoureux
Alcatel-Lucent
Centre De Villarceaux,
France
Email: martin.vigoureux@alcatel-lucent.fr
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