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
Copyright Notice
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Expiration Date
April 2007
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