Retiring TLVs from the Associated Channel Header of the MPLS Generic Associated Channel
draft-ietf-mpls-retire-ach-tlv-02
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draft-farbryantrel-mpls-retire-ach-tlv
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Network Working Group A. Farrel
Internet Draft Juniper Networks
Category: Standards Track S. Bryant
Updates: 5586 (if approved) Cisco Systems
Expires: December 28, 2013 June 28, 2013
Retiring TLVs from the Associated Channel Header of the MPLS Generic
Associated Channel
draft-ietf-mpls-retire-ach-tlv-02.txt
Abstract
The MPLS Generic Associated Channel (G-ACh) is a generalization of
the applicability of the Pseudowire (PW) Associated Channel Header
(ACH). RFC 5586 defines the concept of TLV constructs that can be
carried in messages on the G-ACh by placing them in the ACH between
the fixed header fields and the G-ACh message. These TLVs are called
ACH TLVs
No Associated Channel Type yet defined uses an ACH TLV. Furthermore,
it is believed that handling TLVs in hardware introduces significant
problems to the fast-path, and since G-ACh messages are intended to
be processed substantially in hardware, the use of ACH TLVs is
undesirable.
This document updates RFC 5586 by retiring ACH TLVs and removing the
associated registry.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Farrel and Bryant Expires December 2013 [Page 1]
draft-ietf-mpls-retire-ach-tlv-02.txt June 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction and Scope
RFC4385 [RFC4385] says that if the first nibble of a PW packet
carried over an MPLS network has a value of 1 then the packet starts
with a specific header format called the Pseudowire Associated
Channel Header, known as the PWACH or more generally as the ACH. This
mechanism creates an Associated Channel that is a message channel
associated with a specific pseudowire (PW).
The applicability of the ACH is generalized in RFC 5586 [RFC5586] to
define the MPLS Generic Associated Channel (G-ACh). This creates a
common encapsulation header for control channel messages associated
with MPLS Sections, Label Switching Paths (LSPs), and PWs.
As part of making the ACH fully generic, RFC 5586 defines ACH TLV
constructs. According to RFC 5586:
In some applications of the generalized associated control channel,
it is necessary to include one or more ACH TLVs to provide
additional context information to the G-ACh packet.
RFC 5586 goes on to say:
If the G-ACh message MAY be preceded by one or more ACH TLVs, then
this MUST be explicitly specified in the definition of an ACH
Channel Type.
However, at the time of writing, of the 18 ACH Channel Types defined,
none allows the use of ACH TLVs [IANA-ACH]. At the time of writing
there are no live Internet-Drafts that utilize ACH TLVs.
Furthermore, G-ACh packets are intended to be substantially processed
in hardware, however, processing TLVs in hardware can be hard because
Farrel and Bryant Expires December 2013 [Page 2]
draft-ietf-mpls-retire-ach-tlv-02.txt June 2013
of the unpredictable formats and lengths that they introduce to the
normal ACH format.
This document states that ACH TLVs as specified in RFC 5586 are not
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