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RFC 4863 - Wildcard Pseudowire Type


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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

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].

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.

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.

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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Acknowledgement

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

 

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