Packet Pseudowire Encapsulation over an MPLS PSN
RFC 6658

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

   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
   PWs.

   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
   UK

   EMail: stbryant@cisco.com

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

   EMail: lmartini@cisco.com

   George Swallow
   Cisco Systems
   1414 Massachusetts Ave
   Boxborough, MA  01719
   USA

   EMail: swallow@cisco.com

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

   EMail: andrew.g.malis@verizon.com

Bryant, et al.               Standards Track                   [Page 15]