RFC5994: Application of Ethernet Pseudowires to MPLS Transport Networks
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Related keywords:
(MPLS-TP)
Internet Engineering Task Force (IETF) S. Bryant, Ed.
Request for Comments: 5994 M. Morrow
Category: Informational G. Swallow
ISSN: 2070-1721 Cisco Systems
R. Cherukuri
Juniper Networks
T. Nadeau
Huawei Technologies
N. Harrison
BT
B. Niven-Jenkins
Velocix
October 2010
Application of Ethernet Pseudowires to MPLS Transport Networks
Abstract
Ethernet pseudowires are widely deployed to support packet transport
of Ethernet services. These services in-turn provide transport for a
variety of client networks, e.g., IP and MPLS. This document uses
procedures defined in the existing IETF specifications of Ethernet
pseudowires carried over MPLS networks.
Many of the requirements for the services provided by the mechanisms
explained in this document are also recognized by the MPLS transport
profile (MPLS-TP) design effort formed jointly by the IETF and ITU-T.
The solution described here does not address all of the MPLS-TP
requirements, but it provides a viable form of packet transport
service using tools that are already available.
This document also serves as an indication that existing MPLS
techniques form an appropriate basis for the design of a fully-
featured packet transport solution addressing all of the requirements
of MPLS-TP.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
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Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5994.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. PWE3 Configuration . . . . . . . . . . . . . . . . . . . . . . 5
3. Operations, Administration, and Maintenance (OAM) . . . . . . 5
3.1. VCCV Profile 1: BFD without IP/UDP Headers . . . . . . . . 6
3.2. VCCV Profile 2: BFD with IP/UDP Headers . . . . . . . . . 6
4. MPLS Layer . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. External Configuration . . . . . . . . . . . . . . . . . . 6
4.2. Control Plane Configuration . . . . . . . . . . . . . . . 7
5. Congestion Considerations . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Ethernet pseudowires are widely deployed to support packet transport
of Ethernet services. These services in-turn provide transport for a
variety of client networks, e.g., IP and MPLS. This document uses
procedures defined in the existing IETF specifications of Ethernet
pseudowires carried over MPLS networks.
Many of the requirements for the services provided by the mechanisms
explained in this document are also recognized by the MPLS transport
profile (MPLS-TP) design effort formed jointly by the IETF and ITU-T
[RFC5654]. For example, the ability to operate solely with network
management control, the ability to use Operations, Administration,
and Maintenance (OAM) that does not rely on IP forwarding, and the
ability to provide light-weight proactive connection verification
(CV) functionality.
The solution described in this document does not address all of the
MPLS-TP requirements, but it provides a viable form of packet
transport service using tools that are already available.
The key purpose of this document is to demonstrate that there is an
existing IETF mechanism with known implementations that satisfies the
requirements posed by the operator community. It is recognized that
it is possible to design a more efficient method of satisfying the
requirements, and the IETF anticipates that improved solutions will
be proposed in the future as part of the MPLS-TP effort. Indeed, the
solution described in this document is not intended to detract from
the MPLS-TP effort. Instead, it provides legitimacy for that work by
showing that there is a real demand from networks that are already
deployed, and by indicating that the MPLS-TP solutions work is based
on sound foundations.
Much of the notation used in this document is defined in [RFC3985] to
which the reader is referred for definitions.
The architecture required for this mechanism is illustrated in Figure
1.
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+----------------------------------------------------------------+
| |
| IP/MPLS PSN (PHP may be enabled) |
| (client) |
| |
| +---------------------------+ |
| | | |
| | MPLS PSN (No PHP) | |
| | (server) | |
| | | |
| CE1 |PE1 PE2| CE2 |
| +-----+ +-----+ +-----+ +-----+ |
| | | | | | | | | | | | | | | | | |
| | | | +------+ | | | | | | +------+ | | | |
| | | | | 802.3| | | | | | | | 802.3| | | | |
| +-----+ +-----+ +-----+ +-----+ |
| | | | | | | | | |
| | | +-- ---------------------- -+ | | |
+----- --- -------- -- ---------------------- - -------- --- ----+
| | | |<--MPLS LSP (no PHP)->| | | |
| | | | (server) | | | |
| | | | | |
| | |<------------PW----------->| | |
| | | (server) | | |
| | | |
| |<-------------802.3 (Ethernet)-------------->| |
| | (client) | |
| |
|<---------IP/MPLS LSP (PHP may be supported)-------->|
| (client) |
Figure 1: Application Ethernet over MPLS PW to MPLS Transport
Networks
An 802.3 (Ethernet) circuit is established between CE1 and CE2. This
circuit may be used for the concurrent transport of MPLS packets as
well as IPv4 and IPv6 packets. The MPLS packets may carry IPv4,
IPV6, or pseudowire payloads, and Penultimate Hop Popping (PHP) may
be used. For clarity, these paths are labeled as the client in
Figure 1.
An Ethernet pseudowire (PW) is provisioned between PE1 and PE2 and is
used to carry the Ethernet from PE1 to PE2. The Ethernet PW is
carried over an MPLS Packet Switched Network (PSN), but this PSN MUST
NOT be configured with PHP. For clarity, this Ethernet PW and the
MPLS PSN are labeled as the server in Figure 1. In the remainder of
this document, call the server network a transport network.
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1.1. Requirements Language
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 [RFC2119].
2. PWE3 Configuration
The PWE3 encapsulation used by this specification to satisfy the
transport requirement is Ethernet [RFC4448]. This is used in "raw"
mode.
The Control Word MUST be used. The sequence number MUST be zero.
The use of the Pseudowire Setup and Maintenance Label Distribution
Protocol [RFC4447] is not required by the profile of the PWE3
Ethernet pseudowire functionality defined in this document.
The pseudowire label is statically provisioned.
3. Operations, Administration, and Maintenance (OAM)
Within a connection, traffic units sent from the single source are
constrained to stay within the connection under defect-free
conditions. During misconnected defects, a connection can no longer
be assumed to be constrained, and traffic units (and by implication
also OAM packets) can 'leak' unidirectionally outside a connection.
Therefore, during a misconnected state, it is not possible to rely on
OAM, which relies on a request/response mechanism, and, for this
reason, such OAM should be treated with caution if used for
diagnostic purposes.
Further, when implementing an Equal Cost Multipath (ECMP) function
with MPLS, use of the label stack as the path selector such that the
OAM and data are not in a co-path SHOULD be avoided, as any failure
in the data path will not be reflected in the OAM path. Therefore,
an OAM that is carried within the data-path below the PW label (such
as Virtual Circuit Connectivity Verification (VCCV)) is NOT
vulnerable to the above failure mode. For these reasons, the OAM
mechanism is as described in [RFC5085], which uses Bidirectional
Forwarding Detection (BFD) [RFC5880] for connection verification
(CV). The method of using BFD as a CV method in VCCV is described in
[RFC5885]. One of the VCCV profiles described in Section 3.1 or
Section 3.2 MUST be used. Once a VCCV control channel is provisioned
and the operational status of the PW is UP, no other profile should
be used until such time as the PW's operational status is set to
DOWN.
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3.1. VCCV Profile 1: BFD without IP/UDP Headers
When PE1 and PE2 are not IP capable or have not been configured with
IP addresses, the following VCCV mechanism SHOULD be used.
The connection verification method used by VCCV is BFD with
diagnostics as defined in [RFC5885].
[RFC5085] specifies that the first nibble is set to 0x1 to indicate a
channel associated with a pseudowire [RFC4385].
The Version and the Reserved fields are set to zero, and the Channel
Type is set to 0x7 to indicate that the payload carried is BFD
without IP/UDP headers, as is defined in [RFC5885].
3.2. VCCV Profile 2: BFD with IP/UDP Headers
When PE1 and PE2 are IP capable and have been configured with IP
addresses, the following VCCV mechanism may be used.
The connection verification method used by VCCV is BFD with
diagnostics as defined in [RFC5885].
[RFC5085] specifies that the first nibble is set to 0x1 to indicate a
channel associated with a pseudowire [RFC4385].
The Version and the Reserved fields are set to 0, and the Channel
Type is set to 0x21 for IPv4 and 0x56 for IPv6 payloads [RFC4446].
4. MPLS Layer
The architecture of MPLS-enabled networks is described in [RFC3031].
This section describes a subset of the functionality of the MPLS-
enabled PSN. There are two cases that need to be considered:
1. The case where external configuration is used.
2. The case where a control plane is available.
Where the use of a control plane is desired, this may be based on
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945].
4.1. External Configuration
The use of external provisioning is not precluded from being
supported by the current MPLS specifications. It is however
explicitly described in this specification to address the
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requirements specified by the ITU [RFC5654] to address the needs in a
transport environment.
The MPLS encapsulation is specified in [RFC3032]. All MPLS labels
used in the server layer (Figure 1) MUST be statically provisioned.
Labels may be selected from either the per-platform or the per-
interface label space.
All transport Label Switched Paths (LSPs) utilized by the PWs
described in Section 2 MUST support both unidirectional and
bidirectional point-to-point connections.
The transport LSPs SHOULD support unidirectional point-to-multipoint
connections.
The forward and backward directions of a bidirectional connection
SHOULD follow a symmetrically routed (reciprocal) LSP in the server
network.
Equal Cost Multipath (ECMP) load balancing MUST NOT be configured on
the transport LSPs utilized by the PWs described in Section 2.
The merging of Label Switched Paths is prohibited and MUST NOT be
configured for the transport LSPs utilized by the PWs described in
Section 2.
Penultimate hop popping by the transport Label Switched Routers
(LSRs) MUST be disabled on transport LSPs.
Both EXP-Inferred-PSC LSPs (E-LSP) and Label-Only-Inferred-PSC LSPs
(L-LSP) MUST be supported as defined in [RFC3270].
For the MPLS EXP field [RFC3270] [RFC5462], only the pipe and short-
pipe models are supported.
4.2. Control Plane Configuration
In this section, we describe the control plane configuration when
[RFC3209] or the bidirectional support in GMPLS ([RFC3471] and
[RFC3473]) are used to configure the transport MPLS PSN. When these
protocols are used to provide the control plane, the following are
automatically provided:
1. There is no label merging unless it is deliberately enabled to
support Fast Re-route (FRR) [RFC3209].
2. A single path is provided end-to-end (there is no ECMP).
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3. Label Switched Paths may be unidirectional or bidirectional as
required.
Additionally, the following configuration restrictions required to
support external configuration MUST be applied:
o Penultimate hop popping [RFC3031] by the LSRs MUST be disabled on
LSPs providing PWE3 transport network functionality.
o Both E-LSP and L-LSP MUST be supported as defined in [RFC3270].
o The MPLS EXP [RFC5462] field is supported according to [RFC3270]
only when the pipe and short-pipe models are utilized.
5. Congestion Considerations
This document describes a method of using the existing PWE3 Ethernet
pseudowire [RFC4448] to solve a particular network application. The
congestion considerations associated with that pseudowire and all
subsequent work on congestion considerations regarding Ethernet
pseudowires are applicable to this RFC.
6. Security Considerations
This RFC provides a description of the use of existing IETF Proposed
Standards to solve a network problem, and raises no new security
issues.
The PWE3 security considerations are described in [RFC3985] and the
Ethernet pseudowire security considerations of [RFC4448].
The Ethernet pseudowire is transported on an MPLS PSN; therefore, the
security of the pseudowire itself will only be as good as the
security of the MPLS PSN. The server MPLS PSN can be secured by
various methods, as described in [RFC3031].
The use of static configuration exposes an MPLS PSN to a different
set of security risks to those found in a PSN using dynamic routing.
If a path is misconfigured in a statically configured network, the
result can be a persistent black hole, or much worse, a persistent
forwarding loop. On the other hand, most of the distributed
components are less complex. This is however offset by the need to
provide fail-over and redundancy in the management and configuration
system and the communications paths between those central systems and
the LSRs.
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Security achieved by access control of media access control (MAC)
addresses, and the security of the client layers, is out of the scope
of this document.
7. Acknowledgements
The authors wish to thank Matthew Bocci, John Drake, Adrian Farrel,
Andy Malis, and Yaakov Stein for their review and proposed
enhancements to the text.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, May 2002.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
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[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June 2010.
8.2. Informative References
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
Authors' Addresses
Stewart Bryant (editor)
Cisco Systems
250, Longwater, Green Park
Reading RG2 6GB
UK
EMail: stbryant@cisco.com
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Monique Morrow
Cisco Systems
Glatt-com
CH-8301 Glattzentrum
Switzerland
EMail: mmorrow@cisco.com
George Swallow
Cisco Systems
1414 Massachusetts Ave.
Boxborough, MA 01719
EMail: swallow@cisco.com
Rao Cherukuri
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
EMail: cherukuri@juniper.net
Thomas D. Nadeau
Huawei Technologies
Central Expressway
Santa Clara, CA 95050
EMail: thomas.nadeau@huawei.com
Neil Harrison
BT
EMail: neil.2.harrison@bt.com
Ben Niven-Jenkins
Velocix
326 Science Park
Milton Road, Cambridge CB4 0WG
UK
EMail: ben@niven-jenkins.co.uk
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