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Extended Administrative Groups in MPLS-TE

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7308.
Author Eric Osborne
Last updated 2014-04-22 (Latest revision 2014-04-21)
Replaces draft-osborne-mpls-extended-admin-groups
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Loa Andersson
Shepherd write-up Show Last changed 2014-03-29
IESG IESG state Became RFC 7308 (Proposed Standard)
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Telechat date (None)
Responsible AD Adrian Farrel
Send notices to,
IANA IANA review state IANA - Review Needed
Network Working Group                                         E. Osborne
Intended status: Standards Track                          April 21, 2014
Expires: October 23, 2014

               Extended Administrative Groups in MPLS-TE


   MPLS-TE advertises 32 administrative groups (commonly referred to as
   "colors" or "link colors") using the Administrative Group sub-TLV of
   the Link TLV.  This is defined for OSPFv2 (RFC3630), OSPFv3 (RFC5329)
   and ISIS (RFC5305).

   This document adds a sub-TLV to the IGP TE extensions, "Extended
   Administrative Group".  This sub-TLV provides for additional
   administrative groups (link colors) beyond the current limit of 32.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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."

   This Internet-Draft will expire on October 23, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extended Administrative Groups sub-TLV  . . . . . . . . . . .   3
     2.1.  Packet Format . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Admin group numbering . . . . . . . . . . . . . . . . . .   4
     2.3.  Backward compatability  . . . . . . . . . . . . . . . . .   4
       2.3.1.  AG and EAG coexistence  . . . . . . . . . . . . . . .   4
       2.3.2.  Desire for unadvertised EAG bits  . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Do we need more than 32 bits?

   The IGP extensions to support MPLS-TE (RFCs 3630 [RFC3630] and 5305
   [RFC5305]) define a link TLV known as Administrative Group (AG) with
   a limit of 32 AGs per link.  The concept of Administrative Groups
   comes from section 6.2 of RFC 2702 [RFC2702], which calls them
   Resource Classes.  RFCs 3630 [RFC3630] and 5305 [RFC5305] describe
   the mechanics of the TLV and use the term Administrative Groups
   (sometimes abbreviated herein as AGs), as does this document.

   Networks have grown over time, and MPLS-TE has grown right along with
   them.  Administrative Groups are advertised as a fixed-length 32-bit
   bitmask.  This can be quite constraining, as it is possible to run
   out of vaues rather quickly.  One such use case is #5 in Section 6.2
   of RFC 2702 [RFC2702], using AGs to constrain traffic within specific
   topological regions of the network.  A large network may well have
   far more than 32 geographic regions.  One particular operator builds
   their network along the lines of this use case, using AGs to flag
   network regions down to the metro scale, e.g. Seattle, San Francisco,

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   Dallas, Chicago, St. Louis, etc.  MPLS-TE tunnels are then specified
   with affinities to include or exclude specific metro regions in their
   path calculation.  Each metro region is given its own bit in the AG
   bitmask.  This means that 32 bits can only (cleanly) represent 32
   metro areas.  It should be obvious that 32 may not be enough even for
   a US-based network, nevermind a worldwide network.

   There may be some opportunity for color reuse; that is, bit 0x8 may
   mean 'Seattle' or 'Prague' or 'Singapore' depending on the geography
   in which it is used.  In practice, coordinating this reuse is fraught
   with peril and the reuse effectively becomes the limiting factor in
   MPLS-TE deployment.  With this example it is not possible to build an
   LSP which avoids Seattle while including Prague, as it is the same AG

   This document provides Extended Administrative Groups (EAGs).  The
   number of EAGs has no fixed limit, it is constrained only by
   protocol-specific restrictions such as LSA or MTU size.  While an
   operator may one day need to go beyond these protocol-specific
   restrictions, allow for an arbitrary number of EAGs should easily
   provide the operator with hundreds or thousands of bit values, thus
   no longer making the number of AGs an impediment to network growth.

   EAG's intended use case is within a single domain.  As such, this
   document provides no support for signaling EAG.  It provides no
   analog to either the SESSION_ATTRIBUTE of C-Type 1 defined in
   [RFC3209], nor the LSPA object of the Path Computation Element
   Communication Protocol (PCEP) defined in [RFC5440].

2.  Extended Administrative Groups sub-TLV

   This document defines a sub-TLV of the Link TLV for both OSPF
   [RFC3630] and ISIS [RFC5305] called the Extended Administrative
   Groups (EAG) sub-TLV.  The EAG sub-TLV is used in addition to the
   Administrative Groups when a node wishes to advertise more than 32
   colors for a link.  The EAG sub-TLV is optional.  Coexistence of EAG
   and AG TLVs is covered in Section 2.3.1 of this document.

   This document uses the term 'colors' as a shorthand to refer to
   particular bits with an AG or EAG.  The examples in this document use
   'red' to represent the least significant bit in the AG (red == 0x1),
   'blue' to represent the second bit (blue == 0x2).  To say that a link
   has a given color or that the specified color is set on the link is
   to say that the corresponding bit or bits in the link's AG are set to

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2.1.  Packet Format

   The format of the Extended Administrative Groups sub-TLV is the same
   for both OSPF and ISIS:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       |                   Extended Admin Group                        |
       |                        ...........                            |
       |                   Extended Admin Group                        |

   The Type of the sub-TLV for OSPF and ISIS is TBD.  The Length is the
   size of the Extended Admin Group (EAG) value in bytes.  The EAG may
   be of any non-zero length, but MUST be a multiple of 4 bytes.  The
   only limits on EAG size are those which are imposed by protocol-
   specific or media-specific constraints (e.g. max packet length).

2.2.  Admin group numbering

   By convention, the existing Administrative Group TLVs are numbered 0
   (LSB) to 31 (MSB).  The EAG values are a superset of AG.  That is,
   bits 0-31 in the EAG have the same meaning and MUST have the same
   values as an AG flooded for the same link.  If an EAG's length is
   more than 4 bytes, numbering for these additional bytes picks up
   where the previous byte left off.  For example, the least significant
   bit in the 5th byte of an 8-byte EAG is referred to as bit 32.

2.3.  Backward compatability

   There are two questions to consider for backward compatibility with
   existing AG implementations - how do AG and EAG coexist, and what
   happens if a node has matching criteria for unadvertised EAG bits?

2.3.1.  AG and EAG coexistence

   If a node advertises EAG it MAY also advertise AG.

   If a node advertises both AG and EAG then the first 32 bits of the
   EAG MUST be identical to the advertised AG.

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   If both an AG and EAG are present, a receiving node MUST use the AG
   as the first 32 bits (0-31) of administrative color and use the EAG
   for bits 32 and higher if present.

   A receiving node that notices that the AG differs from the first 32
   bits of the EAG, SHOULD report this mismatch to the operator.

   This process allows nodes which do not support EAG to obtain some
   link color information from the network, but also allow for an
   eventual migration away from AG.

2.3.2.  Desire for unadvertised EAG bits

   The existing AG sub-TLV is optional; thus a node may be configured
   with a preference to include red or exclude blue, and be faced with a
   link that is not advertising a value for either blue or red.  What
   does an implementation do in this case?  It shouldn't assume that red
   is set, but it is also arguably incorrect to assume that red is NOT
   set, as a bit must first exist before it can be set to 0.

   Practically speaking this has not been an issue for deployments, as
   many implementations always advertise the AG bits, often with a
   default value of 0x00000000.  However, this issue may be of more
   concern once EAGs are added to the network.  EAGs may exist on some
   nodes but not others, and the EAG length may be longer for some links
   than for others.

   Each implementation is free to choose its own method for handling
   this question.  However, to allow for maximum interoperability an
   implementation SHOULD treat desired but unadvertised EAG bits as if
   they are set to 0.  Consider the case where a node wants to only use
   links where the 127th bit of an EAG is set to 1.  If a link is only
   advertising 64 EAG bits, clearly the 127th EAG bit is not defined -
   that is, it is neither explicitly 0 nor 1.  The node which wants the
   127th EAG bit to be 1 MUST NOT use this link when implementing the
   recommended behavior, as the assumption is than an unadvertised bit
   is set to 0.

   A node MAY provide other strategies for handling this case.  A
   strategy which deviates from the recommended behavior in this
   document SHOULD be configurable, in order to provide maximum

3.  Security Considerations

   This extension adds no new security considerations.

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4.  IANA Considerations

   This document requests a sub-TLV allocation in both OSPF and ISIS.

   For OSPF, the name space is "Types for sub-TLVs of TE Link TLV (Value
   2)" in the "Open Shortest Path First (OSPF) Traffic Engineering

   For ISIS, it is "Sub-TLVs for TLV 22, 141, and 222" in the "IS-IS TLV
   Codepoints" registry.  For IS-IS the value should be marked 'y' for
   Sub-TLVs 22, 141 and 222; this is identical to the allocation for the
   Administrative Group sub-TLV (value 3).

   In both registries the first free value should be assigned.  As of
   this writing, that's 26 in the OSPF registry and 14 in the IS-IS
   registry.  The Sub-TLV should be caled "Extended Administrative

5.  Acknowledgements

   Thanks to Santiago Alvarez, Rohit Gupta, Liem Nguyen, Tarek Saad,
   Robert Sawaya, Andy Malis, Les Ginsberg and Adrian Farrel for their
   review and comments.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630, September

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440, March

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6.2.  Informative References

   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, September 1999.

Author's Address

   Eric Osborne


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