





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.

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
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   publication of this document.  Please review these 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.

   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



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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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