    Network Working Group                                         L. Martini
    Request for Comments: 4863                                    G. Swallow
    Category: Standards Track                            Cisco Systems, Inc.
                                                                    May 2007

                            Wildcard Pseudowire Type

    Status of This Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The IETF Trust (2007).

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

    Table of Contents

       1. Introduction ....................................................2
          1.1. Conventions and Terminology ................................2
       2. Wildcard PW Type ................................................3
       3. Procedures ......................................................3
          3.1. Procedures When Sending the Wildcard FEC ...................3
          3.2. Procedures When Receiving the Wildcard FEC .................3
       4. Security Considerations .........................................4
       5. IANA Considerations .............................................4
       6. References ......................................................4
          6.1. Normative References .......................................4
          6.2. Informative References .....................................4

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    RFC 4863                Wildcard Pseudowire Type                May 2007

    1.  Introduction

       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.

       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
       that lacks configuration must wait to receive a Label Mapping message
       in order to learn the PW Type, prior to signaling its unidirectional
       LSP.

       For certain applications this can become particularly onerous.  For
       example, suppose that an ingress Provider Edge (PE) is serving as
       part of a gateway function between a layer 2 network and layer 2
       attachment circuits 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.  However, this information is known at the PE supporting the
       targeted attachment circuit.

       In this situation, it is often desirable to allow the initiation of
       the two LSPs that compose a pseudowire to remain independent.  A
       means is needed for allowing a PW endpoint (lacking a priori
       knowledge of the PW Type) to initiate the creation of an LSP.  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)
       Architecture" [ARCH].

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    RFC 4863                Wildcard Pseudowire Type                May 2007

    2.  Wildcard PW Type

       In order to allow a PE to initiate the signaling exchange for a
       pseudowire without knowing the pseudowire type, a new PW Type is
       defined.  The codepoint is 0x7FFF.  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 that is not configured to use a specific PW Type for a
       particular pseudowire wishes to signal an LSP for that pseudowire, 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 a Label Mapping message indicating the
       wildcard PW Type, it follows the normal procedures for checking the
       Attachment Group Identifier (AGI) and Target Attachment Individual
       Identifier (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
       Misconfiguration Error".

       Otherwise, it treats the Label Mapping message as if it had indicated
       the PW Type it is configured to use.

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    RFC 4863                Wildcard Pseudowire Type                May 2007

    4.  Security Considerations

       This document 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
       security considerations of [CONTROL], in general, and those
       pertaining to the Generalized PWid FEC Element, in particular.

    5.  IANA Considerations

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

             PW Type        Description

             0x7FFF         Wildcard

    6.  References

    6.1.  Normative References

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

       [CONTROL]    Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T.,
                    and G. Heron, "Pseudowire Setup and Maintenance Using
                    the Label Distribution Protocol (LDP)", RFC 4447, April
                    2006.

       [IANA]       Martini, L., "IANA Allocations for Pseudowire Edge to
                    Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

    6.2.  Informative References

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

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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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    RFC 4863                Wildcard Pseudowire Type                May 2007

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       Funding for the RFC Editor function is currently provided by the
       Internet Society.

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