draft-ietf-mpls-retire-ach-tlv-03.txt   rfc7026.txt 
Network Working Group A. Farrel Internet Engineering Task Force (IETF) A. Farrel
Internet Draft Juniper Networks Request for Comments: 7026 Juniper Networks
Category: Standards Track S. Bryant Updates: 5586 S. Bryant
Updates: 5586 (if approved) Cisco Systems Category: Standards Track Cisco Systems
Expires: January 31, 2014 July 31, 2013 ISSN: 2070-1721 September 2013
Retiring TLVs from the Associated Channel Header of the MPLS Generic
Associated Channel
draft-ietf-mpls-retire-ach-tlv-03.txt Retiring TLVs from the Associated Channel Header
of the MPLS Generic Associated Channel
Abstract Abstract
The MPLS Generic Associated Channel (G-ACh) is a generalization of The MPLS Generic Associated Channel (G-ACh) is a generalization of
the applicability of the Pseudowire (PW) Associated Channel Header the applicability of the pseudowire (PW) Associated Channel Header
(ACH). RFC 5586 defines the concept of TLV constructs that can be (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 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 the fixed header fields and the G-ACh message. These TLVs are called
ACH TLVs ACH TLVs
No Associated Channel Type yet defined uses an ACH TLV. Furthermore, No Associated Channel Type yet defined uses an ACH TLV. Furthermore,
it is believed that handling TLVs in hardware introduces significant it is believed that handling TLVs in hardware introduces significant
problems to the fast-path, and since G-ACh messages are intended to problems to the fast path, and since G-ACh messages are intended to
be processed substantially in hardware, the use of ACH TLVs is be processed substantially in hardware, the use of ACH TLVs is
undesirable. undesirable.
This document updates RFC 5586 by retiring ACH TLVs and removing the This document updates RFC 5586 by retiring ACH TLVs and removing the
associated registry. associated registry.
Status of this Memo 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 This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
http://www.ietf.org/ietf/1id-abstracts.txt (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.
The list of Internet-Draft Shadow Directories can be accessed at Information about the current status of this document, any
http://www.ietf.org/shadow.html errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7026.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
1. Introduction and Scope 1. Introduction and Scope
RFC4385 [RFC4385] says that if the first nibble of a PW packet 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 carried over an MPLS network has a value of 1, then the packet starts
with a specific header format called the Pseudowire Associated with a specific header format called the Pseudowire Associated
Channel Header, known as the PWACH or more generally as the ACH. This Channel Header (PWACH) or more generally known as the ACH. This
mechanism creates an Associated Channel that is a message channel mechanism creates an Associated Channel that is a message channel
associated with a specific pseudowire (PW). associated with a specific pseudowire (PW).
The applicability of the ACH is generalized in RFC 5586 [RFC5586] to The applicability of the ACH is generalized in RFC 5586 [RFC5586] to
define the MPLS Generic Associated Channel (G-ACh). This creates a define the MPLS Generic Associated Channel (G-ACh). This creates a
common encapsulation header for control channel messages associated common encapsulation header for control channel messages associated
with MPLS Sections, Label Switching Paths (LSPs), and PWs. with MPLS Sections, Label Switching Paths (LSPs), and PWs.
As part of making the ACH fully generic, RFC 5586 defines ACH TLV As part of making the ACH fully generic, RFC 5586 defines ACH TLV
constructs. According to RFC 5586: constructs. According to RFC 5586:
skipping to change at page 2, line 48 skipping to change at page 2, line 48
it is necessary to include one or more ACH TLVs to provide it is necessary to include one or more ACH TLVs to provide
additional context information to the G-ACh packet. additional context information to the G-ACh packet.
RFC 5586 goes on to say: RFC 5586 goes on to say:
If the G-ACh message MAY be preceded by one or more ACH TLVs, then 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 this MUST be explicitly specified in the definition of an ACH
Channel Type. Channel Type.
However, at the time of writing, of the 18 ACH Channel Types defined, 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 none allows the use of ACH TLVs [IANA-ACH]. At the time of writing,
there are no live Internet-Drafts that utilize ACH TLVs. there are no unexpired Internet-Drafts that utilize ACH TLVs.
Furthermore, G-ACh packets are intended to be substantially processed Furthermore, G-ACh packets are intended to be substantially processed
in hardware, however, processing TLVs in hardware can be hard because in hardware; however, processing TLVs in hardware can be difficult
of the unpredictable formats and lengths that they introduce to the because of the unpredictable formats and lengths that they introduce
normal ACH format. to the normal ACH format.
This document states that ACH TLVs as specified in RFC 5586 are not 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 useful and might be harmful. It updates RFC 5586 by deprecating the
ACH TLV and updating the associated IANA registries as described in ACH TLV and updating the associated IANA registries as described in
Section 4 of this document. This document makes no comment about the Section 4 of this document. This document makes no comment about the
use of TLVs in other places. In particular, proposals to use TLVs use of TLVs in other places. In particular, proposals to use TLVs
within ACH messages or as an appendage to ACH messages, are not in within ACH messages or as an appendage to ACH messages, are not in
scope of this document. scope of this document.
1.1. Specification of Requirements 1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Update to RFC 5586 2. Update to RFC 5586
Section 3 of RFC 5586 is deleted. Section 3 of RFC 5586 is deleted.
References to ACH TLVs in Section 4 of RFC 5586 should also be References to ACH TLVs in Section 4 of RFC 5586 should also be
disregarded. Note that the text in Section 4 currently uses phrases disregarded. Note that the text in Section 4 currently uses phrases
like "ACH TLV(s), if present" so, with the removal of Section 3 that like "ACH TLV(s), if present" so, with the removal of Section 3 that
used to define ACH TLVs, they will not be present. used to define ACH TLVs, they will not be present.
3. Implication for the ACH 3. Implication for the ACH
A G-ACh message MUST NOT be preceded by an ACH TLV. A G-ACh message MUST NOT be preceded by an ACH TLV.
4. IANA Considerations 4. IANA Considerations
This document requests IANA to make two changes to the IANA
registries.
4.1. Associated Channel Header TLV Registry
The "Pseudowire Name Spaces (PWE3)" registry has a sub-registry This document details two changes to the IANA registries.
called the "Associated Channel Header TLV Registry". IANA is
requested to entirely delete this sub-registry, but to leave a
tombstone record in the top-level list of registries that says:
Associated Channel Header TLV Registry RFC 5586 RFC xxxx 4.1. Associated Channel Header TLV Registry
Where "xxxx" is the number of this RFC. The "Pseudowire Name Spaces (PWE3)" registry has a subregistry called
the "Associated Channel Header TLV Registry". IANA has entirely
deleted this subregistry but has left a tombstone record in the top-
level list of registries that says:
draft-ietf-mpls-retire-ach-tlv-03.txt July 20 13 Associated Channel Header TLV Registry (DELETED)
4.2. Pseudowire Associated Channel Types Registry Reference
[RFC5586] [RFC7026]
The "Pseudowire Name Spaces (PWE3)" registry has a sub-registry 4.2. Pseudowire Associated Channel Types Registry
called the "Pseudowire Associated Channel Types Registry". This
sub-registry includes a column marked "TLV Follows". IANA is
requested to entirely delete this column leaving no record.
IANA is requested to add a pointer to this RFC in the definition of The "Pseudowire Name Spaces (PWE3)" registry has a subregistry
this sub-registry. called the "Pseudowire Associated Channel Types" registry. This
subregistry previously included a column marked "TLV Follows".
IANA has entirely deleted this column leaving no record.
5. Manageability Considerations 5. Manageability Considerations
This document will have no impact on network or device manageability This document will have no impact on network or device
because there are no ACH Types that allow the use of TLVs. manageability because there are no ACH Types that allow the use of
The document removes a feature that might have been used to enhance TLVs. The document removes a feature that might have been used to
management messages, and especially Operations, Management, and enhance management messages, and especially Operations, Management,
Administration (OAM) messages. However, given the considerable and Administration (OAM) messages. However, given the considerable
experience in defining MPLS OAM messages in the last few years, it experience in defining MPLS OAM messages in the last few years, it
would appear that this feature is not useful. would appear that this feature is not useful.
It is possible that packet sniffers that have already been It is possible that packet sniffers that have already been
implemented will look for ACH TLVs. The deletion of the construct implemented will look for ACH TLVs. The deletion of the construct
will not have a negative impact. will not have a negative impact.
6. Security Considerations 6. Security Considerations
Deleting the ACH TLV has a marginal positive effect on security Deleting the ACH TLV has a marginal positive effect on security
because it removes a feature that might have been used as an attack because it removes a feature that might have been used as an attack
vector to carry false information or to bloat G-ACh messages. vector to carry false information or to bloat G-ACh messages.
On the other hand, it had been sugested that the ACH TLV could have On the other hand, it had been suggested that the ACH TLV could
been used to carry security parameters to secure the messages on the have been used to carry security parameters to secure the messages
G-ACh in a generic way. However, no mechanisms have been proposed at on the G-ACh in a generic way. However, no mechanisms have been
the time of writing, and it has generally been considered that it is proposed at the time of writing, and it has generally been
the responsiblity of the specification that defines G-ACh messages to considered that it is the responsibility of the specification that
consider the security requirements of those messages which may be defines G-ACh messages to consider the security requirements of
different for the different applications. those messages that may be different for the different
applications.
Otherwise, this document has no implications for security. Otherwise, this document has no implications for security.
7. Acknowledgements 7. Acknowledgements
Thanks to Eric Osborne, Thomas Morin, Lizhong Jin, Greg Mirsky, Jia Thanks to Eric Osborne, Thomas Morin, Lizhong Jin, Greg Mirsky, Jia
He, and Pearl Liang for suggestions to improve the text. He, and Pearl Liang for suggestions to improve the text.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, [RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
for Use over an MPLS PSN", RFC 4385, February 2006. Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
Associated Channel", RFC 5586, June 2009. "MPLS Generic Associated Channel", RFC 5586, June 2009.
8.2. Informative References 8.2. Informative References
[IANA-ACH] "Pseudowire Associated Channel Types", IANA, [IANA-ACH] "Pseudowire Associated Channel Types", IANA,
http://www.iana.org/assignments/pwe3-parameters/pwe3- <http://www.iana.org/assignments/pwe3-parameters>
parameters.xml#pwe3-parameters-10
Authors' Addresses Authors' Addresses
Adrian Farrel Adrian Farrel
Juniper Networks Juniper Networks
EMail: adrian@olddog.co.uk EMail: adrian@olddog.co.uk
Stewart Bryant Stewart Bryant
Cisco Systems Cisco Systems
EMail: stbryant@cisco.com EMail: stbryant@cisco.com
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