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Versions: 00 01 02 RFC 4863

Network Working Group                                       Luca Martini
Internet Draft                                       Cisco Systems, Inc.
Category: Standards Track
Expiration Date: April 2007
                                                          George Swallow
                                                     Cisco Systems, Inc.

                                                            October 2006


                        Wildcard Pseudowire Type


                draft-ietf-pwe3-wildcard-pw-type-02.txt

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Abstract

   Pseudowire signaling requires that the Pseudowire Type (PW Type) be
   identical in both directions.  For certain applications the
   configuration of the PW Type is most easily accomplished by
   configuring this information at just one PW endpoint.  In any form of
   LDP-based signaling, each PW endpoint must initiate the creation of a
   unidirectional LSP.  In order to allow the initiation of these two
   LSPs to remain independent, a means of allowing the PW endpoint



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   lacking a priori knowledge of the PW Type to initiate the creation of
   an LSP is needed.  This document defines a Wildcard PW Type to
   satisfy this need.




Contents

 1      Introduction  ..............................................   3
 1.1    Conventions and Terminology  ...............................   3
 2      Wildcard PW Type  ..........................................   4
 3      Procedures  ................................................   4
 3.1    Procedures when sending the wildcard FEC  ..................   4
 3.2    Procedures when receiving the wildcard FEC  ................   4
 4      Security Considerations  ...................................   5
 5      IANA Considerations  .......................................   5
 6      References  ................................................   5

































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1. Introduction

   Pseudowire signaling requires that the Pseudowire Type (PW Type) be
   identical in both directions.  For certain applications the configu-
   ration of the PW Type is most easily accomplished by configuring this
   information at just one PW endpoint.  In any form of LDP-based sig-
   naling, each PW endpoint must initiate the creation of a unidirec-
   tional LSP.

   By the procedures of [CONTROL] both label mapping messages must carry
   the PW type and the two unidirectional mapping messages must be in
   agreement.  Thus within the current procedures the PW endpoint which
   lacks configuration must wait to receive a Label Mapping message in
   order to learn the PW Type, prior signaling the its unidirectional
   LSP.

   For certain applications this can become particularly onerous.  For
   example, suppose that an ingress PE is serving as part of a gateway
   function between a layer two network and layer two attachment cir-
   cuits on remote PEs.  Suppose further that the initial setup needs to
   be initiated from the layer 2 network, but the layer 2 signaling does
   not contain sufficient information to determine the PW Type.  This
   information, however is known at the PE supporting the targeted
   attachment circuit.

   In this situation it is often desirable to allow the initiation of
   the initiation of the two LSPs which compose a pseudowire to remain
   independent.  A means of allowing a PW endpoint lacking a piori
   knowledge of the PW Type to initiate the creation of an LSP is
   needed.  This document defines a wildcard PW Type to satisfy this
   need.




1.1. Conventions and Terminology

   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 [KEYWORDS].

   This document introduces no new terminology.  However it assumes that
   the reader is familiar with the terminology contained in [CONTROL]
   and RFC 3985, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architec-
   ture" [ARCH].






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2. Wildcard PW Type

   In order to allow a PE to initiate the signaling exchange for a pseu-
   dowire without knowing the pseudowire type, a new PW Type is defined.
   The proposed codepoint is 0x7fff [to be assigned by IANA].  The
   semantics are the following:

   1.  To the targeted PE, this value indicates that it is to determine
       the PW Type (for both directions) and signal that in a label
       mapping message back to the initiating PE.

   2.  For the procedures of [CONTROL] this PW Type is interpreted to
       match any PW Type other than itself.  That is the targeted PE may
       respond with any valid PW Type other than the wildcard PW Type.


3. Procedures

3.1. Procedures when sending the wildcard FEC

   When a PE which is not configured to use a specific PW Type for a
   particular pseudowire, wishes to signaling an LSP for that pseu-
   dowire, it sets the PW Type to "wildcard".  This indicates that the
   target PE should determine the PW Type for this pseudowire.

   When a Label Mapping message is received for the pseudowire, the PE
   checks the PW Type.

   If the PW Type can be supported, the PE uses this as the PW Type for
   both directions.

   If the PW Type cannot be supported or is "wildcard" it MUST respond
   to this message with a Label Release message with an LDP Status Code
   of "Generic Misconfiguration Error".  Further actions are beyond the
   scope of this document but could include notifying the associated
   application (if any) or notifying network management.


3.2. Procedures when receiving the wildcard FEC

   When a targeted PE receives Label Mapping message indicating the
   wildcard PW Type, it follows the normal procedures for checking the
   AGI and TAII values.  If the targeted PE is not configured to use a
   specific, non-wildcard PW Type it MUST respond to this message with a
   Label Release message with an LDP Status Code of "Generic Misconfigu-
   ration Error".

   Otherwise it treats the Label Mapping message as if it had indicated



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   the PW Type it is configured to use.



4. Security Considerations

   This draft has little impact on the security aspects of [CONTROL].
   The message exchanges remain the same.  However a malicious agent
   attempting to connect to an access circuit would require one less
   piece of information.  To mitigate against this, a pseudowire control
   entity receiving a request containing the wildcard FEC type SHOULD
   only proceed with setup if explicitly configured to do so for the
   particular AI in the TAI.  Further, the reader should note the secu-
   rity considerations of [CONTROL] in general and those pertaining to
   the Generalized ID FEC Element in particular.


5. IANA Considerations

   This document requests the following allocation be made from the IETF
   consensus range of the "Pseudowire Type" registry as defined in
   [IANA].

         PW Type        Description

         0x7FFF (TBA)   Wildcard


6. References

Normative References

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

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

   [CONTROL]    Martini, L., et al., "Pseudowire Setup and
                Maintenance using the Label Distribution Protocol",
                RFC 4447, April 2006.

   [IANA]       Martini, L., and Townsley, M., "IANA Allocations for
                pseudo Wire Edge to Edge Emulation (PWE3)",
                RFC 4447, April 2006.





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Authors' Addresses

      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



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Expiration Date

   April 2007


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