Retiring TLVs from the Associated Channel Header of the MPLS Generic Associated Channel
RFC 7026
| Document | Type |
RFC - Proposed Standard
(September 2013; No errata)
Updates RFC 5586
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-farbryantrel-mpls-retire-ach-tlv | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Loa Andersson | ||
| Shepherd write-up | Show (last changed 2013-07-11) | ||
| IESG | IESG state | RFC 7026 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Spencer Dawkins | ||
| Send notices to | (None) | ||
| IANA | IANA review state | IANA OK - Actions Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) A. Farrel
Request for Comments: 7026 Juniper Networks
Updates: 5586 S. Bryant
Category: Standards Track Cisco Systems
ISSN: 2070-1721 September 2013
Retiring TLVs from the Associated Channel Header
of the MPLS Generic Associated Channel
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 is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 5741.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7026.
Farrel & Bryant Standards Track [Page 1]
RFC 7026 Retiring ACH TLVs September 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
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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
RFC 4385 [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 (PWACH) or more generally known 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 unexpired Internet-Drafts that utilize ACH TLVs.
Farrel & Bryant Standards Track [Page 2]
RFC 7026 Retiring ACH TLVs September 2013
Furthermore, G-ACh packets are intended to be substantially processed
in hardware; however, processing TLVs in hardware can be difficult
because 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
useful and might be harmful. It updates RFC 5586 by deprecating the
ACH TLV and updating the associated IANA registries as described in
Section 4 of this document. This document makes no comment about the
use of TLVs in other places. In particular, proposals to use TLVs
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