RFC 4859 INFORMATIONAL RSVP · MPLS · IANA

Codepoint Registry for the Flags Field in the Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Session Attribute Object

A registry for the flag bits in RSVP-TE session messages

On rfc-editor.org ↗
PUBLISHED
April 2007
AUTHORS
A. Farrel
STREAM
IETF
FLAGS FIELD WIDTH
8 bits
BITS IN USE
6 (0x01, 0x02, 0x04, 0x08, 0x10, 0x20)
ASSIGNMENT POLICY
IETF consensus (RFC 2434)
DOI
10.17487/RFC4859

RFC text

Contents
Original text · RFC Editor View on rfc-editor.org ↗
Network Working Group                                          A. Farrel
Request for Comments: 4859                            Old Dog Consulting
Category: Informational                                       April 2007


               Codepoint Registry for the Flags Field in
    the Resource Reservation Protocol-Traffic Engineering (RSVP-TE)
                        Session Attribute Object

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document provides instructions to IANA for the creation of a new
   codepoint registry for the flags field in the Session Attribute
   object of the Resource Reservation Protocol Traffic Engineering
   (RSVP-TE) signaling messages used in Multiprotocol Label Switching
   (MPLS) and Generalized MPLS (GMPLS) signaling.

1.  Introduction

   The Resource Reservation Protocol (RSVP) [RFC2205] has been extended
   as RSVP for Traffic Engineering (RSVP-TE) for use in Multiprotocol
   Label Switching (MPLS) signaling [RFC3209] and Generalized MPLS
   (GMPLS) [RFC3473].

   [RFC3209] introduced a new signaling object, the Session Attribute
   object, that is carried on the RSVP Path message.  The Session
   Attribute object contains an eight-bit field of flags.

   The original specification of RSVP-TE assigned uses to three of these
   bit flags.  Subsequent MPLS and GMPLS RFCs have assigned further
   flags.

   There is a need for a codepoint registry to track the use of the bit
   flags in this field, to ensure that bits are not assigned more than
   once, and to define the procedures by which such bits may be
   assigned.

   This document lists the current bit usage and provides information
   for IANA to create a new registry.  This document does not define the
   uses of specific bits -- definitive procedures for the use of the
   bits can be found in the referenced RFCs.

2.  Existing Usage

2.1.  RFC 3209

   [RFC3209] defines the use of three bits as follows:

   0x01  Local protection desired

   0x02  Label recording desired

   0x04  SE Style desired

2.2.  RFC 4090

   [RFC4090] defines the use of two bits as follows:

   0x08  Bandwidth protection desired

   0x10  Node protection desired

2.3.  RFC 4736

   [RFC4736] defines the use of one bit as follows:

   0x20  Path re-evaluation request

3.  Security Considerations

   This informational document exists purely to create an IANA registry.
   Such registries help to protect the IETF process against denial-of-
   service attacks.

   Otherwise there are no security considerations for this document.

4.  IANA Considerations

   IANA has created a new codepoint registry as follows.

   The new registry has been placed under the "RSVP-TE Parameters"
   branch of the tree.

   The new registry has been termed "Session Attribute Object Flags."

   Flags from this registry may only be assigned by IETF consensus
   [RFC2434].

   The registry references the flags already defined as described in
   Section 2 of this document.

5.  Acknowledgements

   Thanks to JP Vasseur, Bill Fenner, and Thomas Narten for reviewing
   this document.

6.  References

6.1.  Normative References

   [RFC2205]   Braden, R., Ed., Zhang, L., Berson, S., Herzog, S. and S.
               Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
               1, Functional Specification", RFC 2205, September 1997.

   [RFC2434]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 2434,
               October 1998.

   [RFC3209]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.

   [RFC3473]   Berger, L., Ed., "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling - Resource ReserVation
               Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
               3473, January 2003.

6.2.  Informative References

   [RFC4090]   Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
               Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
               May 2005.

   [RFC4736]   Vasseur, JP., Ed., Ikejiri, Y., and R. Zhang,
               "Reoptimization of Multiprotocol Label Switching (MPLS)
               Traffic Engineering (TE) Loosely Routed Label Switched
               Path (LSP)", RFC 4736, November 2006.

Author's Address

   Adrian Farrel
   Old Dog Consulting

   EMail: adrian@olddog.co.uk

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
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Acknowledgement

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

AI ELI5

On this page
PROBLEMRSVP-TE (Resource Reservation Protocol for Traffic Engineering) includes an 8-bit flags field in its Session Attribute object. As MPLS and GMPLS protocols evolved, different RFCs assigned uses to different bits, with no central registry to prevent conflicts.
MECHANISMRFC 4859 lists the existing bit assignments from earlier RFCs and asks IANA to create a new codepoint registry to track which bits mean what, ensuring no bit is assigned twice and defining clear procedures for future assignments.
WHY IT MATTERSA formal registry prevents bit conflicts and makes it clear how engineers should request new bits. IETF consensus is required to assign new flags.

§1The Problem and the Solution

RSVP-TE is used to set up label-switched paths (LSPs) in MPLS and GMPLS networks. It extends the original RSVP with traffic engineering features. The Session Attribute object in an RSVP-TE Path message carries an 8-bit field of flags, where each bit can mean "yes, please do this" for a particular feature.

RFC 3209 defined three of these bits. Later, RFC 4090 added two more, and RFC 4736 added one more. Without a registry, the next RFC writer might not know which bits were already used, and accidentally reuse a bit for something different. RFC 4859 solves this by asking IANA to create and manage the registry.

The message has eight lights, and different engineers had been turning on different lights for different reasons. This note says let's make an official list so nobody gets confused.

§2What the Bits Mean Today

From RFC 3209: bit 0x01 means "local protection desired", 0x02 means "label recording desired", 0x04 means "SE Style desired". From RFC 4090: 0x08 means "bandwidth protection desired", 0x10 means "node protection desired". From RFC 4736: 0x20 means "path re-evaluation request".

This gives IANA a starting list. Future RFCs can request new bits from the unassigned ones (0x40, 0x80, etc.).

Some bits already mean: protect along a backup route, record the labels, protect bandwidth, protect nodes, and ask for a fresh calculation of the best route.

§3How New Flags Are Assigned

New flags can only be assigned through IETF consensus, as defined in RFC 2434. This high bar ensures that every new feature gets careful review from the Internet engineering community before a bit is permanently allocated to it.

The registry is placed under the "RSVP-TE Parameters" branch in IANA's tree of registries. Anyone who needs a new flag must make a case to the IETF that it is necessary and well-designed.

If someone needs to turn on a new light, they have to convince the whole Internet engineering community that it's a good idea, so we don't run out of lights for silly reasons.

§4References