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rfc:rfc4863

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

Martini & Swallow Standards Track [Page 1] 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].

Martini & Swallow Standards Track [Page 2] 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.

Martini & Swallow Standards Track [Page 3] 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.

Martini & Swallow Standards Track [Page 4] RFC 4863 Wildcard Pseudowire Type May 2007

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

Martini & Swallow Standards Track [Page 5] RFC 4863 Wildcard Pseudowire Type May 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

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

Martini & Swallow Standards Track [Page 6]

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