[RFC Home] [TEXT|PDF|HTML] [Tracker] [IPR] [Info page]

Internet Engineering Task Force (IETF)                    S. Bryant, Ed.
Request for Comments: 6658                                    L. Martini
Category: Standards Track                                     G. Swallow
ISSN: 2070-1721                                            Cisco Systems
                                                                A. Malis
                                                  Verizon Communications
                                                               July 2012

            Packet Pseudowire Encapsulation over an MPLS PSN


   This document describes a pseudowire mechanism that is used to
   transport a packet service over an MPLS PSN in the case where the
   client Label Switching Router (LSR) and the server Provider Edge
   equipments are co-resident in the same equipment.  This pseudowire
   mechanism may be used to carry all of the required layer 2 and layer
   3 protocols between the pair of client LSRs.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2012 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.

Bryant, et al.               Standards Track                    [Page 1]

RFC 6658                        Packet PW                      July 2012

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Network Reference Model  . . . . . . . . . . . . . . . . . . .  4
   3.  Client Network-Layer Model . . . . . . . . . . . . . . . . . .  5
   4.  Forwarding Model . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Packet PW Encapsulation  . . . . . . . . . . . . . . . . . . .  7
   6.  Ethernet and IEEE 802.1 Functional Restrictions  . . . . . . .  8
   7.  Congestion Considerations  . . . . . . . . . . . . . . . . . .  8
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     11.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     11.2. Informative References . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Encapsulation Approaches Considered . . . . . . . . . 11
     A.1.  A Protocol Identifier in the Control Word  . . . . . . . . 11
     A.2.  PID Label  . . . . . . . . . . . . . . . . . . . . . . . . 12
     A.3.  Parallel PWs . . . . . . . . . . . . . . . . . . . . . . . 13
     A.4.  Virtual Ethernet . . . . . . . . . . . . . . . . . . . . . 13
     A.5.  Recommended Encapsulation  . . . . . . . . . . . . . . . . 14

Bryant, et al.               Standards Track                    [Page 2]

RFC 6658                        Packet PW                      July 2012

1.  Introduction

   There is a need to provide a method of carrying a packet service over
   an MPLS PSN in a way that provides isolation between the two
   networks.  The server MPLS network may be an MPLS network or a
   network conforming to the MPLS Transport Profile (MPLS-TP) [RFC5317].
   The client may also be either an MPLS network or a network conforming
   to the MPLS-TP.  Considerations regarding the use of an MPLS network
   as a server for an MPLS-TP network are outside the scope of this

   Where the client equipment is connected to the server equipment via a
   physical interface, the same data-link type must be used to attach
   the clients to the Provider Edge (PE) equipments, and a pseudowire
   (PW) of the same type as the data-link must be used [RFC3985].  The
   reason that interworking between different physical and data-link
   attachment types is specifically disallowed in the pseudowire
   architecture is because this is a complex task and not a simple bit-
   mapping exercise.  The interworking is not limited to the physical
   and data-link interfaces and the state-machines.  It also requires a
   compatible approach to the formation of the adjacencies between
   attached client network equipment.  As an example, the reader should
   consider the differences between router adjacency formation on a
   point-to-point link compared to a multipoint-to-multipoint interface
   (e.g., Ethernet).

   A further consideration is that two adjacent MPLS Label Switching
   Routers (LSRs) do not simply exchange MPLS packets.  They exchange IP
   packets for adjacency formation, control, routing, label exchange,
   management, and monitoring purposes.  In addition, they may exchange
   data-link packets as part of routing (e.g., IS-IS Hellos and IS-IS
   Link State Packets) and for Operations, Administration, and
   Maintenance (OAM) purposes such as the Link-Layer Discovery Protocol
   [IEEE.802.1AB.2009].  Thus, the two clients require an attachment
   mechanism that can be used to multiplex a number of protocols.  In
   addition, it is essential to the correct operation of the network
   layer that all of these protocols fate share.

   Where the client LSR and server PE are co-located in the same
   equipment, the data-link layer can be simplified to a point-to-point
   Ethernet used to multiplex the various data-link types onto a
   pseudowire.  This is the method described in this document.

   Appendix A provides information on alternative approaches to
   providing a packet PW that were considered by the PWE3 Working Group
   and the reasons for using the method defined in this specification.

Bryant, et al.               Standards Track                    [Page 3]

RFC 6658                        Packet PW                      July 2012

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Network Reference Model

   The network reference model for the packet pseudowire operating in an
   MPLS network is shown in Figure 1.  This is an extension of Figure 3
   "Pre-processing within the PWE3 Network Reference Model" from

                  PW                            PW
               End Service                   End Service
                   |                            |
                   |<------- Pseudowire ------->|
                   |                            |
                   |          Server            |
                   |     |<- PSN Tunnel ->|     |
                   |     V                V     |
   -------   +-----+-----+                +-----+-----+   -------
          )  |     |     |================|     |     |  (
   Client  ) | MPLS| PE1 |      PW1       | PE2 | MPLS| ( Client
   MPLS PSN )+ LSR1+............................+ LSR2+( MPLS PSN
           ) |     |     |                |     |     | (
          )  |     |     |================|     |     |  (
   -------   +-----+-----+                +-----+-----+   --------
                   ^                            ^
                   |                            |
                   |                            |
                   |<---- Emulated Service----->|
                   |                            |
            Virtual physical             Virtual physical
               termination                  termination

                Figure 1: Packet PW Network Reference Model

   In this model, the LSRs (LSR1 and LSR2) are part of the client MPLS
   PSN.  The PEs (PE1 and PE2) are part of the server PSN that is to be
   used to provide connectivity between the client LSRs.  The attachment
   circuit that is used to connect the MPLS LSRs to the PEs is a virtual
   interface within the equipment.  A packet pseudowire is used to
   provide connectivity between these virtual interfaces.  This packet
   pseudowire is used to transport all of the required layer 2 and layer
   3 protocols between LSR1 and LSR2.

Bryant, et al.               Standards Track                    [Page 4]

RFC 6658                        Packet PW                      July 2012

3.  Client Network-Layer Model

   The packet PW appears as a single point-to-point link to the client
   layer.  Network-layer adjacency formation and maintenance between the
   client equipments will follow the normal practice needed to support
   the required relationship in the client layer.  The assignment of
   metrics for this point-to-point link is a matter for the client
   layer.  In a hop-by-hop routing network, the metrics would normally
   be assigned by appropriate configuration of the embedded client
   network-layer equipment (e.g., the embedded client LSR).  Where the
   client was using the packet PW as part of a traffic-engineered path,
   it is up to the operator of the client network to ensure that the
   server-layer operator provides the necessary service-level agreement.

4.  Forwarding Model

   The packet PW forwarding model is illustrated in Figure 2.  The
   forwarding operation can be likened to a virtual private network
   (VPN), in which a forwarding decision is first taken at the client
   layer, an encapsulation is applied, and then a second forwarding
   decision is taken at the server layer.

            |                                                |
            |  +--------+                        +--------+  |
            |  |        |   Pkt   +-----+        |        |  |
         ------+        +---------+ PW1 +--------+        +------
            |  | Client |    AC   +-----+        | Server |  |
     Client |  | LSR    |                        | LSR    |  | Server
    Network |  |        |   Pkt   +-----+        |        |  | Network
         ------+        +---------+ PW2 +--------+        +------
            |  |        |    AC   +-----+        |        |  |
            |  +--------+                        +--------+  |
            |                                                |

                   Figure 2: Packet PW Forwarding Model

   A packet PW PE comprises three components: the client LSR, a PW
   processor, and a server LSR.  Note that [RFC3985] does not formally
   indicate the presence of the server LSR because it does not concern
   itself with the server layer.  However it is useful in this document
   to recognize that the server LSR exists.

   It may be useful to first recall the operation of a layer 2 PW such
   as an Ethernet PW [RFC4448] within this model.  The client LSR is not
   present, and packets arrive directly on the attachment circuit (AC)
   that is part of the client network.  The PW function undertakes any

Bryant, et al.               Standards Track                    [Page 5]

RFC 6658                        Packet PW                      July 2012

   header processing, if configured to do so; it then optionally pushes
   the PW control word (CW) and finally pushes the PW label.  The PW
   function then passes the packet to the LSR function, which pushes the
   label needed to reach the egress PE and forwards the packet to the
   next hop in the server network.  At the egress PE, the packet
   typically arrives with the PW label at the top of the stack; the
   packet is thus directed to the correct PW instance.  The PW instance
   performs any required reconstruction using, if necessary, the CW, and
   the packet is sent directly to the attachment circuit.

   Now let us consider the case of client-layer MPLS traffic being
   carried over a packet PW.  An LSR belonging to the client layer is
   embedded within the PE equipment.  This is a type of native service
   processing element [RFC3985].  The client LSR determines the next hop
   in the client layer, and pushes the label needed by the next hop in
   the client layer.  It then encapsulates the packet in an Ethernet
   header setting the Ethertype to MPLS, and the client LSR passes the
   packet to the correct PW instance.  The PW instance then proceeds as
   defined for an Ethernet PW [RFC4448] by optionally pushing the
   control word, then pushing the PW label, and finally handing the
   packet to the server-layer LSR for delivery to the egress PE in the
   server layer.

   At the egress PE in the server layer, the packet is first processed
   by the server LSR, which uses the PW label to pass the packet to the
   correct PW instance.  This PW instance processes the packet as
   described in [RFC4448].  The resultant Ethernet encapsulated client
   packet is then passed to the egress client LSR, which then processes
   the packet in the normal manner.

   Note that although the description above is written in terms of the
   behavior of an MPLS LSR, the processing model would be similar for an
   IP packet or any other protocol type.

   Note that the semantics of the PW between the client LSRs is a point-
   to-point link.

Bryant, et al.               Standards Track                    [Page 6]

RFC 6658                        Packet PW                      July 2012

5.  Packet PW Encapsulation

   The client network-layer packet encapsulation into a packet PW is
   shown in Figure 3.

   |            Client             |
   |          Network-Layer        |
   |            Packet             |  n octets
   |                               |
   |                               |
   |          Ethernet             | 14 octets
   |           Header              |
   |               +---------------+
   |               |
   |    Optional Control Word      |  4 octets
   |          PW Label             |  4 octets
   |   Server MPLS Tunnel Label(s) |  n*4 octets (4 octets per label)

                     Figure 3: Packet PW Encapsulation

   This conforms to the PW protocols stack as defined in [RFC4448].  The
   protocol stack is unremarkable except to note that the stack does not
   retain 32-bit alignment between the virtual Ethernet header and the
   PW optional control word (or the PW label when the optional
   components are not present in the PW header).  This loss of 32 bits
   of alignment is necessary to preserve backwards compatibility with
   the Ethernet PW design [RFC4448]

   Ethernet Raw Mode (PW type 5) MUST be used for the packet PW.

   The PEs MAY use a local Ethernet address for the Ethernet header used
   to encapsulate the client network-layer packet or MAY use the special
   Ethernet addresses "PacketPWEthA" or "PacketPWEthB" as described

   IANA has allocated two unicast Ethernet addresses [RFC5342] for use
   with this protocol, referred to as "PacketPWEthA" and "PacketPWEthB".
   Where [RFC4447] signaling is used to set up the PW, the LDP peers
   numerically compare their IP addresses.  The LDP PE with the higher-
   value IP address will use PacketPWEthA, whilst the LDP peer with the
   lower-value IP address uses PacketPWEthB.

Bryant, et al.               Standards Track                    [Page 7]

RFC 6658                        Packet PW                      July 2012

   Where no signaling PW protocol is used, suitable Ethernet addresses
   MUST be configured at each PE.

   Although this PW represents a point-to-point connection, the use of a
   multicast destination address in the Ethernet encapsulation is
   REQUIRED by some client-layer protocols.  Peers MUST be prepared to
   handle a multicast destination address in the Ethernet encapsulation.

6.  Ethernet and IEEE 802.1 Functional Restrictions

   The use of Ethernet as the encapsulation mechanism for traffic
   between the server LSRs is a convenience based on the widespread
   availability of existing hardware.  In this application, there is no
   requirement for any Ethernet feature other than its protocol
   multiplexing capability.  Thus, for example, a server LSR is not
   required to implement the Ethernet OAM.

   The use and applicability of VLANs, IEEE 802.1p, and IEEE 802.1Q
   tagging between PEs is not supported.

   Point-to-multipoint and multipoint-to-multipoint operation of the
   virtual Ethernet is not supported.

7.  Congestion Considerations

   A packet pseudowire is normally used to carry IP, MPLS and their
   associated support protocols over an MPLS network.  There are no
   congestion considerations beyond those that ordinarily apply to an IP
   or MPLS network.  Where the packet protocol being carried is not IP
   or MPLS and the traffic volumes are greater than that ordinarily
   associated with the support protocols in an IP or MPLS network, the
   congestion considerations developed for PWs apply [RFC3985]

8.  Security Considerations

   The virtual Ethernet approach to packet PW introduces no new security
   risks.  A more detailed discussion of pseudowire security is given in
   [RFC3985], [RFC4447], and [RFC3916].

Bryant, et al.               Standards Track                    [Page 8]

RFC 6658                        Packet PW                      July 2012

9.  IANA Considerations

   IANA has allocated two Ethernet unicast addresses from "IANA Unicast
   48-bit MAC Addresses".

   Address              Usage             Reference
   -------------------  ----------------  ---------
   00-00-5E-00-52-00    PacketPWEthA      [RFC6658]
   00-00-5E-00-52-01    PacketPWEthB      [RFC6658]

10.  Acknowledgements

   The authors acknowledge the contributions made to this document by
   Sami Boutros, Giles Herron, Siva Sivabalan, and David Ward.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC5342]  Eastlake, D., "IANA Considerations and IETF Protocol Usage
              for IEEE 802 Parameters", BCP 141, RFC 5342,
              September 2008.

11.2.  Informative References

              Institute of Electrical and Electronics Engineers, "IEEE
              Standard for Local and Metropolitan Area Networks --
              Station and Media Access Control Connectivity Discovery",
              IEEE Standard 802.1AB, 2009.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3916]  Xiao, X., McPherson, D., and P. Pate, "Requirements for
              Pseudo-Wire Emulation Edge-to-Edge (PWE3)", RFC 3916,
              September 2004.

Bryant, et al.               Standards Track                    [Page 9]

RFC 6658                        Packet PW                      July 2012

   [RFC3985]  Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
              Edge (PWE3) Architecture", RFC 3985, March 2005.

   [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.

   [RFC5317]  Bryant, S. and L. Andersson, "Joint Working Team (JWT)
              Report on MPLS Architectural Considerations for a
              Transport Profile", RFC 5317, February 2009.

   [RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
              October 2009.

   [RFC5921]  Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
              Berger, "A Framework for MPLS in Transport Networks",
              RFC 5921, July 2010.

Bryant, et al.               Standards Track                   [Page 10]

RFC 6658                        Packet PW                      July 2012

Appendix A.  Encapsulation Approaches Considered

   A number of approaches to the design of a packet pseudowire (PW) were
   investigated by the PWE3 Working Group and were discussed in IETF
   meetings and on the PWE3 list.  This section describes the approaches
   that were analyzed and the technical issues that the authors took
   into consideration in arriving at the approach described in the main
   body of this document.  This appendix is provided so that engineers
   considering alternative optimizations can have access to the
   rationale for the selection of the approach described in this

   In a typical network, there are usually no more that four network-
   layer protocols that need to be supported: IPv4, IPv6, MPLS, and
   Connectionless Network Service (CLNS).  However, any solution needs
   to be scalable to a larger number of protocols.  The approaches
   considered in this appendix all satisfy this minimum requirement but
   vary in their ability to support larger numbers of network-layer

   Additionally, it is beneficial if the complete set of protocols
   carried over the network in support of a set of CE peers fate share.
   It is additionally beneficial if a single OAM session can be used to
   monitor the behavior of this complete set.  During the investigation,
   various views were expressed as to where these benefits lay on the
   scale from absolutely required to "nice to have", but in the end,
   they were not a factor in reaching our conclusion.

   Four candidate approaches were analyzed:

   1.  A protocol identifier (PID) in the PW control word (CW)

   2.  A PID label

   3.  Parallel PWs - one per protocol

   4.  Virtual Ethernet

A.1.  A Protocol Identifier in the Control Word

   In this approach, a Protocol Identifier (PID) is included in the PW
   control word (CW) by appending it to the generic control word
   [RFC4385] to make a 6-byte CW (it was thought that this approach
   would include 2 reserved bytes to provide 32-bit alignment, but then
   this was optimized out).  A variant of this is just to use a 2-byte
   PID without a control word.

Bryant, et al.               Standards Track                   [Page 11]

RFC 6658                        Packet PW                      July 2012

   This is a simple approach and is basically a virtual PPP interface
   without the PPP control protocol.  This has a smaller MTU than, for
   example, a virtual Ethernet would need; however, in forwarding terms,
   it is not as simple as the PID label or multiple PW approaches
   described next and may not be deployable on a number of existing
   hardware platforms.

A.2.  PID Label

   In this approach, the PID is indicated by including a label after the
   PW label that indicates the protocol type, as shown in Figure 4.

   |            Client             |
   |          Network-Layer        |
   |            Packet             |  n octets
   |                               |
   |    Optional Control Word      |  4 octets
   |        PID Label (S=1)        |  4 octets
   |          PW Label             |  4 octets
   |   Server MPLS Tunnel Label(s) |  n*4 octets (four octets per label)

               Figure 4: Encapsulation of a Pseudowire with
                     a Pseudowire Load-Balancing Label

   In the PID label approach, a new Label Distribution Protocol (LDP)
   Forwarding Equivalence Class (FEC) element is used to signal the
   mapping between protocol type and the PID label.  This approach
   complies with [RFC3031].

   A similar approach to PID label is described in Section 3.4.5 of
   [RFC5921].  In this case, when the client is a network-layer packet
   service such as IP or MPLS, a service label and demultiplexer label
   (which may be combined) are used to provide the necessary
   identifications needed to carry this traffic over an LSP.

   The authors surveyed the hardware designs produced by a number of
   companies across the industry and concluded that whilst the approach
   complies with the MPLS architecture, it may conflict with a number of
   designers' interpretations of the existing MPLS architecture.  This
   led to concerns that the approach may result in unexpected
   difficulties in the future.  Specifically, there was an assumption in
   many designs that a forwarding decision should be made on the basis

Bryant, et al.               Standards Track                   [Page 12]

RFC 6658                        Packet PW                      July 2012

   of a single label.  Whilst the approach is attractive, it cannot be
   supported by many commodity chip sets, and this would require new
   hardware, which would increase the cost of deployment and delay the
   introduction of a packet PW service.

A.3.  Parallel PWs

   In this approach, one PW is constructed for each protocol type that
   must be carried between the PEs.  Thus, a complete packet PW would
   consist of a bundle of PWs.  This model would be very simple and
   efficient from a forwarding point of view.  The number of parallel
   PWs required would normally be relatively small.  In a typical
   network, there are usually no more that four network-layer protocols
   that need to be supported: IPv4, IPv6, MPLS, and CLNS.  However, any
   solution needs to be scalable to a larger number of protocols.

   There are a number of serious downsides with this approach:

   1.  From an operational point of view, the lack of fate sharing
       between the protocol types can lead to complex faults that are
       difficult to diagnose.

   2.  There is an undesirable trade-off in the OAM related to the first
       point.  We would have to run an OAM on each PW and bind them
       together, which leads to significant protocol and software
       complexity and does not scale well.  Alternatively, we would need
       to run a single OAM session on one of the PWs as a proxy for the
       others and then diagnose any more complex failures on a case-by-
       case basis.  To some extent, the issue of fate sharing between
       protocols in the bundle (for example, the assumed fate sharing
       between CLNS and IP in IS-IS) can be mitigated through the use of
       Bidirectional Forwarding Detection (BFD).

   3.  The need to configure, manage, and synchronize the behavior of a
       group of PWs as if they were a single PW leads to an increase in
       control-plane complexity.

   The Parallel PW mechanism is therefore an approach that simplifies
   the forwarding plane, but only at a cost of a considerable increase
   in other aspects of the design, in particular, operation of the PW.

A.4.  Virtual Ethernet

   Using a virtual Ethernet to provide a packet PW would require PEs to
   include a virtual (internal) Ethernet interface and then to use an
   Ethernet PW [RFC4448] to carry the user traffic.  This is
   conceptually simple and can be implemented today without any further
   standards action, although there are a number of applicability

Bryant, et al.               Standards Track                   [Page 13]

RFC 6658                        Packet PW                      July 2012

   considerations that it are useful to bring to the attention of the

   Conceptually, this is a simple approach, and some deployed equipments
   can already do this.  However, the requirement to run a complete
   Ethernet adjacency led us to conclude that there was a need to
   identify a simpler approach.  The packets encapsulated in an Ethernet
   header have a larger MTU than the other approaches, although this is
   not considered to be an issue on the networks needing to carry packet

   The virtual Ethernet mechanism was the first approach that the
   authors considered, before the merits of the other approaches
   appeared to make them more attractive.  As we shall see below,
   however, the other approaches were not without issues, and it appears
   that the virtual Ethernet is the preferred approach to providing a
   packet PW.

A.5.  Recommended Encapsulation

   The operational complexity and the breaking of fate-sharing
   assumptions associated with the parallel PW approach would suggest
   that this is not an approach that should be further pursued.

   The PID label approach gives rise to the concerns that it will break
   implicit behavioral and label-stack size assumptions in many
   implementations.  Whilst those assumptions may be addressed with new
   hardware, this would delay the introduction of the technology to the
   point where it is unlikely to gain acceptance in competition with an
   approach that needs no new protocol design and is already supportable
   on many existing hardware platforms.

   The PID in the CW leads to the most compact protocol stack, is
   simple, and requires minimal protocol work.  However, it is a new
   forwarding design and, apart from the issue of the larger packet
   header and the simpler adjacency formation, offers no advantage over
   the virtual Ethernet.

   The above considerations bring us back to the virtual Ethernet, which
   is a well-known protocol stack with a well-known (internal) client
   interface.  It is already implemented in many hardware platforms and
   is therefore readily deployable.  After considering a number of
   initially promising alternatives, the authors conclude that the
   simplicity and existing hardware make the virtual Ethernet approach
   to the packet PW the most attractive solution.

Bryant, et al.               Standards Track                   [Page 14]

RFC 6658                        Packet PW                      July 2012

Authors' Addresses

   Stewart Bryant (editor)
   Cisco Systems
   250, Longwater, Green Park,
   Reading, Berks  RG2 6GB

   EMail: stbryant@cisco.com

   Luca Martini
   Cisco Systems
   9155 East Nichols Avenue, Suite 400
   Englewood, CO  80112

   EMail: lmartini@cisco.com

   George Swallow
   Cisco Systems
   1414 Massachusetts Ave
   Boxborough, MA  01719

   EMail: swallow@cisco.com

   Andrew G. Malis
   Verizon Communications
   60 Sylvan Rd.
   Waltham, MA  02451

   EMail: andrew.g.malis@verizon.com

Bryant, et al.               Standards Track                   [Page 15]