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Versions: 00 01 02 03 draft-ietf-mpls-extended-admin-group

Network Working Group                                         E. Osborne
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                           July 12, 2013
Expires: January 13, 2014

               Extended Administrative Groups in MPLS-TE


   This document provides additional administrative groups (sometimes
   referred to as "link colors") to the IGP extensions for MPLS-TE.

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
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   This Internet-Draft will expire on January 13, 2014.

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

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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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Do we need more than 32 bits? . . . . . . . . . . . . . .   2
   2.  Extended Administrative Groups sub-TLV  . . . . . . . . . . .   4
     2.1.  Packet Format . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Admin group numbering . . . . . . . . . . . . . . . . . .   5
     2.3.  Backward compatability  . . . . . . . . . . . . . . . . .   5
       2.3.1.  AG and EAG coexistence  . . . . . . . . . . . . . . .   5
       2.3.2.  Desire for unadvertised EAG bits  . . . . . . . . . .   5
   3.  Attribute filters in RSVP . . . . . . . . . . . . . . . . . .   6
     3.1.  EXTENDED_SESSION_ATTRIBUTE_RA . . . . . . . . . . . . . .   6
     3.2.  Populating the attribute filter fields  . . . . . . . . .   7
     3.3.  Formatting a Path message . . . . . . . . . . . . . . . .   7
     3.4.  Interpreting the attribute filter fields  . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   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.

1.1.  Do we need more than 32 bits?

   The IGP extensions to support MPLS-TE (RFCs 3630 and 5305) define a
   link TLV known as Administrative Group (AG) with a limit of 32 AGs
   per link.  This property comes from section 6.2 of RFC 2702
   [RFC2702].  RFCs 3630 and 5305 describe the mechanics of the TLV; the
   actual definition of the field comes from RFC 2702:


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   "[Administrative Groups] can be used to implement many policies with
   regard to both traffic and resource oriented performance
   optimization.  Specifically,...[AGs] can be used to:

   1.  Apply uniform policies to a set of resources that do not need to
   be in the same topological region.

   2.  Specify the relative preference of sets of resources for path
   placement of traffic trunks.

   3.  Explicitly restrict the placement of traffic trunks to specific
   subsets of resources.

   4.  Implement generalized inclusion / exclusion policies.

   5.  Enforce traffic locality containment policies.  That is, policies
   that seek to contain local traffic within specific topological
   regions of the network.

   Additionally, resource class attributes can be used for
   identification purposes."


   The use of 'Specifically' in RFC2702 is not read as normative; that
   is, the purpose of the quoted text is not to limit the use of AGs to
   the six listed policies, they are given as examples.  However, the
   listed policies make good grounds to justify increasing the limit
   from 32.

   Networks have grown over time, and MPLS-TE has grown right along with
   them.  Implementing all six policies with only 32 bits gives the
   operator only five bits per policy with two bits left over.  This can
   be quite constraining; AGs are a bit mask, so five bits does not mean
   32 possible values, it means 5.  Running a country-wide or world-wide
   MPLS-TE network with only five possible values for each case is
   clearly too constraining.

   Even if an operator wishes to use AGs to implement only a single
   policy it is possible to run out of bit values.  One such use case is
   #5, 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 uses AGs to flag
   network regions down to the metro scale, e.g. Seattle, San Francisco,
   Dallas, Chicago, St. Louis, etc.  MPLS-TE tunnels are then specified
   with affinities to include or exclude specific metro regions in their
   path calculation.  It is clear that 32 may not be enough even for a
   US-based network, nevermind a worldwide network.

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   There may be some opportunity for color reuse; that is, bit 0x8 may
   mean 'Seattle' and 'Prague' and '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 value.

   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.

2.  Extended Administrative Groups sub-TLV

   The Extended Administrative Groups 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.

   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

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                        |

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   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 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.

2.3.  Backward compatability

   There are two things 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.  If the AG and EAG advertised for a
   link differ, the EAG MUST take priority.  This 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.  If a
   node advertises EAG without AG then any receiving node SHOULD alert
   the network operator to this violation via the appropriate mechanism,
   e.g. syslog.

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.

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   Each implementation is free to choose its own method for handling
   this question.  However, to encourage maximum interoperability an
   implementation SHOULD treat specified but unadvertised EAG bits as if
   they are set to 0.  A node MAY provide other (configurable)
   strategies for handling this case.

3.  Attribute filters in RSVP

   In addition to updating the IGP sub-TLV, RSVP needs to be extended to
   provide the ability to signal desired resource affinities.  This
   section provides that update.


   This section provides the EXTENDED_SESSION_ATTRIBUTE_RA.

   [NOTE: This section reads like EXTENDED_SESSION_ATTRIBUTE_RA is
   another C-Type of the SESSION_ATTRIBUTE Class.  Whether it is
   implemented like this or whether it ultimately gets specified as a
   new Class is up for discussion and needs to be resolved prior to
   publication as an RFC.]

   RFC 3209 defines two types of SESSION_ATTRIBUTE, one with resource
   affinities and one without.  The former is C-Type 1 and is referred
   to in this document as SESSION_ATTRIBUTE_RA.  The latter is referred
   to as SESSION_ATTRIBUTE_NO_RA and is C-Type 7.

   The Class and C-Type for EXTENDED_SESSION_ATTRIBUTE_RA are 207 and
   TBD, respectively.  The format of the EXTENDED_SESSION_ATTRIBUTE_RA

    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
   |                  Attribute filter length                      |
   |                                                               |
   //                        Exclude-any                          //
   |                                                               |
   |                                                               |
   //                        Include-any                           //
   |                                                               |
   |                                                               |
   //                        Include-all                          //
   |                                                               |

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   |   Setup Prio  | Holding Prio  |     Flags     |  Name Length  |
   |                                                               |
   //          Session Name      (NULL padded display string)      //
   |                                                               |

   The Exclude-any, Include-any and Include-all fields are collectively
   referred to as the "attribute filter fields".  All three attribute
   filter fields MUST be the same length.  All fields in the
   EXTENDED_SESSION_ATTRIBUTE_RA MUST be interpreted exactly as they are

   The attribute filter length is the sum of the lengths of the three
   attribute filter fields, in bytes.  If the user wishes to convey 128
   bits of information in each of the fields, the total length of the
   attribute filter fields is 3*128 == 384 bits.  The attribute filter
   length is thus 384/8 == 48 bytes.  The next 4 bytes of the
   EXTENDED_SESSION_ATTRIBUTE_RA are fixed - setup priority, holding
   priority, flags and name length - and the remainder of the object is
   the Session Name.  If the user wishes to convey 128 bits of
   information each of the three attribute filter fields and provides a
   64-byte Session Name then the total length of this object in bytes is
   4 + 48 + 4 + 64 == 120 bytes.

3.2.  Populating the attribute filter fields

   Each attribute filter field MUST be the same length.  As with the EAG
   sub-TLV, each attribute filter field is a multiple of four bytes in
   length.  The length of each field MUST be at least the minimum length
   necessary to fully convey the headend's matching criteria, and SHOULD
   be no longer than that.  For example, if the headend wishes to
   Include-any bits 1 and 17 then all three fields MUST be at least 4
   bytes in length and SHOULD be no more than 4 bytes in length.  If the
   headend wishes to Include-any bits 1, 17 and 150 then all three
   fields MUST be at least 20 bytes (160 bits) in length and SHOULD be
   no longer than 20 bytes.

3.3.  Formatting a Path message

   [NOTE: Actual bits and bytes to be sorted out later.  For now, this
   section describes the desired behavior without prescribing specific
   packet formats.  Open questions include - do we need to specify a new
   Class to hold EXTENDED_SESSION_ATTRIBUTE_RA, or can we reuse C-Type?
   What's legal?  What's least likely to break existing implementations?
   Once that's decided, we also need a section on how to handle errors
   such as an invalid combination of resource affinities, etc.)]

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   In order to provide for backward compatibility, a node MAY signal
   allows nodes which understand only SESSION_ATTRIBUTE_RA to use it,
   and nodes which understand EXTENDED_SESSION_ATTRIBUTE_RA (and thus
   also understand SESSION_ATTRIBUTE_RA) to use it.  If a node signals
   first 32 bits of the EXTENDED_SESSION_ATTRIBUTE_RA MUST match the
   SESSION_ATTRIBUTE_RA.  If they do not match, a node SHOULD alert the
   operator as to this mismatch, and MUST ignore the
   This is essentially the same behavior as in section 2.3.1 of this

   A node MUST NOT signal the combination of (SESSION_ATTRIBUTE_NO_RA



   A node MUST NOT signal both SESSION_ATTRIBUTE_RA and

   There are eight combinations of [SESSION_ATTRIBUTE_NO_RA,
   the combination where none of the three is advertised.  Their
   legality is summarized in the following table, using SA_NO_RA, SA_RA
   and ESA_RA as abbreviated column headers:

                  | Valid? | SA_NO_RA | SA_RA | ESA_RA |
                  | Y      | x        |       |        |
                  | Y      |          | x     |        |
                  | Y      |          |       | x      |
                  | Y      |          | x     | x      |
                  | N      | x        | x     |        |
                  | N      | x        |       | x      |
                  | N      | x        | x     | x      |
                  | N      |          |       |        |

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3.4.  Interpreting the attribute filter fields

   Since the attribute filter fields are of variable length, it is
   possible that an RSVP message may indicate more bits than a given
   node has advertised for a link.  It is equally possible that an RSVP
   message may indicate fewer bits than a given node has advertised for
   a link.  In all cases, the shorter of the two fields (the attribute
   filter field or the locally configured link admin group) MUST be
   padded with zeros so that both fields are of equal length.

   Specifically, length mismatches are to be handled as follows:

   The length of any single attribute filter field is A.

   The length of the configured link attribute for a given link is C.

   If C > A, a node MUST pad the received attribute filter field values
   with zeros so that C == A. A node MUST NOT alter the length of the
   signalled attribute filter field; the zero padding is only local to a
   given node.

   If A > C, a node MUST pad the locally configured link attributes with
   zeros so that A == C. A node SHOULD NOT use this information to alter
   the length of the EAG sub-TLV that it floods.

   [ NOTE: rfc3209 is unclear about how the attribute filter fields are
   to be used.  The intent appears to be that any bits set to 1 in any
   of the three attribute filter fields must be considered a match for
   filtering purposes, and that any bits set to 0 are not used to match.
   In other words, there is no way to say "the following bits MUST be
   zero" for any of the attribute filter fields.  A 0 in an attribute
   filter field says "I do not care what the value of this bit is".  I
   am making this inference largely from the text in Include-any and
   Include-all which says "A null set...automatically passes".  If
   existing implementations treat these fields differently (e.g. a 0
   MUST be matched as a zero) then I'd like to know that so I can get
   the text in this section right. ]

4.  Security Considerations

   This extension adds no new security considerations.

5.  IANA Considerations

   This document requests a sub-TLV allocation in both OSPF and ISIS, as
   well as an RSVP C-Type from Class 207.

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6.  Acknowledgements

   Thanks to Santiago Alvarez, Rohit Gupta, Liem Nguyen, Tarek Saad, and
   Robert Sawaya for their review and comments.

7.  Normative References

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

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

   [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.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem,
              "Traffic Engineering Extensions to OSPF Version 3", RFC
              5329, September 2008.

Author's Address

   Eric Osborne
   Cisco Systems

   Email: eosborne@cisco.com

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