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rfc:rfc5994

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.

Bryant, et al. Informational [Page 1] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 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.

Copyright Notice

 Copyright (c) 2010 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
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 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.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

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

Bryant, et al. Informational [Page 2] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

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.

Bryant, et al. Informational [Page 3] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

   +----------------------------------------------------------------+
   |                                                                |
   |                  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.

Bryant, et al. Informational [Page 4] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

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.

Bryant, et al. Informational [Page 5] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

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

Bryant, et al. Informational [Page 6] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 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).

Bryant, et al. Informational [Page 7] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 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.

Bryant, et al. Informational [Page 8] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 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.

Bryant, et al. Informational [Page 9] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 [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

Bryant, et al. Informational [Page 10] RFC 5994 Eth PWs to MPLS Transport Ntwks October 2010

 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

Bryant, et al. Informational [Page 11]

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