[Docs] [txt|pdf|xml] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-bryant-pwe3-packet-pw) 00 01 02 03 04 RFC 6658

Network Working Group                                     S. Bryant, Ed.
Internet-Draft                                                L. Martini
Intended status: Standards Track                              G. Swallow
Expires: November 13, 2012                                 Cisco Systems
                                                                A. Malis
                                                  Verizon Communications
                                                            May 12, 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.

Requirements Language

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

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 13, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Bryant, et al.          Expires November 13, 2012               [Page 1]

Internet-Draft                  Packet PW                       May 2012

   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.

Table of Contents

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

Bryant, et al.          Expires November 13, 2012               [Page 2]

Internet-Draft                  Packet PW                       May 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 equipments (PE)s, and a pseudowire
   (PW) of the same type as the data-link must be used [RFC3985].  The
   reason that inter-working 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 inter-working 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 Link Layer Discovery protocol
   [IEEE standard 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 is 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 that described in this document.

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

Bryant, et al.          Expires November 13, 2012               [Page 3]

Internet-Draft                  Packet PW                       May 2012

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 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 between protocols between LSR1 and LSR2.

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

Bryant, et al.          Expires November 13, 2012               [Page 4]

Internet-Draft                  Packet PW                       May 2012

   client equipments will the follow 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, 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 recognise 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)
   which is part of the client network.  The PW function undertakes any
   header processing, if configured to do so, it then optionally pushes
   the PW control word (CW), and finally pushes the PW label.  The PW

Bryant, et al.          Expires November 13, 2012               [Page 5]

Internet-Draft                  Packet PW                       May 2012

   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 top of 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 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.  The client LSR then 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 processed 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
   behaviour of an MPLS LSR, the processing model would be similar for
   an IP packet, or indeed any other protocol type.

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

5.  Packet PW Encapsulation

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

Bryant, et al.          Expires November 13, 2012               [Page 6]

Internet-Draft                  Packet PW                       May 2012

   |            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 (four 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 bit 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 below.

   IANA is requested to allocate [ed note: RFC Editor will change to
   "has allocated"] two unicast Ethernet addresses [RFC5342] for use
   with this protocol, referred to as "PacketPWEthA" and "PacketPWEthB".
   Where [RFC4447] signalling 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.

   Where no signalling 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

Bryant, et al.          Expires November 13, 2012               [Page 7]

Internet-Draft                  Packet PW                       May 2012

   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].

9.  IANA Considerations

   IANA are requested to allocate two Ethernet unicast addresses from
   the IANA Ethernet Address Block - Unicast Use

Bryant, et al.          Expires November 13, 2012               [Page 8]

Internet-Draft                  Packet PW                       May 2012

   Dotted Decimal       Description       Reference
   -------------------  ----------------  ---------

   000.00x.000          PacketPWEthA      [This RFC]
   000.00x.001          PacketPWEthB      [This RFC]

   The value of x is open for IANA to choose. A value of 3 is suggested.

10.  Acknowledgements

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

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

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

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

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

Bryant, et al.          Expires November 13, 2012               [Page 9]

Internet-Draft                  Packet PW                       May 2012

   [RFC5385]  Touch, J., "Version 2.0 Microsoft Word Template for
              Creating Internet Drafts and RFCs", RFC 5385,
              February 2010.

   [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.

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 analysed 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 rational
   for the selection of the approach described above.

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

   Additionally it is beneficial if the complete set of protocols
   carried over the network between 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 behaviour of this complete set.  During the
   investigation various views were expressed as to where on the scale
   from absolutely required to "nice to have" these benefits lay, but in
   the end they were not a factor in reaching our conclusion.

   There are four candidate approaches that have been analysed:

   1.  A protocol identifier (PID) in the PW Control Word (CW)

   2.  A PID label

   3.  Parallel PWs - one per protocol.

Bryant, et al.          Expires November 13, 2012              [Page 10]

Internet-Draft                  Packet PW                       May 2012

   4.  Virtual Ethernet

A.1.  A Protocol Identifier in the Control Word

   This is the approach that we proposed in draft 0 of this document .
   The proposal was that a Protocol Identifier (PID) would included in
   the PW control word (CW), by appending it to the generic control word
   [RFC5385] to make a 6 byte CW (the version 0 draft actually included
   two reserved bytes to provide 32bit alignment, but let us assume that
   was optimized out).  A variant of this is just to use a 2 byte PID
   without a control word.

   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

A.2.  PID Label

   This is the approach that we described in Version 2 of this document.
   The in this mechanism 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.

Bryant, et al.          Expires November 13, 2012              [Page 11]

Internet-Draft                  Packet PW                       May 2012

   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) is 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
   designer's interpretation of the existing MPLS architecture.  This
   led to concerns that the approach may result in unexpected
   difficulties in the future.  Specifically there is an assumption in
   many designs that a forwarding decision should be made on the basis
   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
   therefore 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
   although any solution needs to be scalable to a larger number of

   The 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 which are
       difficult to diagnose.

   2.  There is an undesirable trade off in the OAM related to the first
       point.  Either we would have to run an OAM on each PW and bind
       them together which lead 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 the diagnose any more complex failure on a case by
       case basis.  To some extent the issue of fate sharing between
       protocol in the bundle (for example the assumed fate sharing
       between CLNS and IP in IS-IS) can be mitigated through the use of

Bryant, et al.          Expires November 13, 2012              [Page 12]

Internet-Draft                  Packet PW                       May 2012

   3.  The need to configure manage and synchronize the behaviour 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 which simplifies
   the forwarding plane, but only at a cost of a considerable increase
   in other aspects of the design and 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
   considerations that it is useful to draw 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 lead 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 preferred approach to providing a packet

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 behavioural 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 was unlikely to gain acceptance in competition with an
   approach that needed 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

Bryant, et al.          Expires November 13, 2012              [Page 13]

Internet-Draft                  Packet PW                       May 2012

   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

   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.  The authors conclude that having
   considered a number of initially promising alternatives, the
   simplicity and existing hardware make the virtual Ethernet approach
   to the packet PW the most attractive solution.

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

Bryant, et al.          Expires November 13, 2012              [Page 14]

Internet-Draft                  Packet PW                       May 2012

   Andy Malis
   Verizon Communications
   117 West St.
   Waltham, MA  02451

   Email: andrew.g.malis@verizon.com

Bryant, et al.          Expires November 13, 2012              [Page 15]

Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/