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Versions: 00 01 02 03 04 05 06 RFC 5384

PIM WG                                                          A. Boers
Internet-Draft                                              IJ. Wijnands
Expires: April 4, 2006                                          E. Rosen
                                                      Cisco Systems, Inc.
                                                             october 2005


                  Format for using TLVs in PIM messages
                    draft-ietf-pim-join-attributes-00

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    This Internet-Draft will expire on April 4, 2006.

Copyright Notice

    Copyright (C) The Internet Society (2005).

Abstract

    This document describes a generic TLV attribute encoding format to be
    added to PIM.








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Table of Contents

    1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
    2.  Use of the Attribute Field in Join Messages . . . . . . . . . . 3
      2.1.  Attribute join  . . . . . . . . . . . . . . . . . . . . . . 3
      2.2.  Transitive attributes . . . . . . . . . . . . . . . . . . . 3
      2.3.  Attribute Hello Option  . . . . . . . . . . . . . . . . . . 3
      2.4.  Conflicting Attributes  . . . . . . . . . . . . . . . . . . 4
      2.5.  Attribute Convergence . . . . . . . . . . . . . . . . . . . 4
      2.6.  Multiple Attributes . . . . . . . . . . . . . . . . . . . . 4
    3.  PIM Attribute packet format . . . . . . . . . . . . . . . . . . 5
      3.1.  PIM Join packet format  . . . . . . . . . . . . . . . . . . 5
      3.2.  PIM Attribute Hello option  . . . . . . . . . . . . . . . . 6
    4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
    5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
      5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
      5.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
    Intellectual Property and Copyright Statements  . . . . . . . . . . 8
































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1.  Introduction

    It is sometimes convenient to add additional information to PIM join
    messages.  The generic PIM encoding format is not always optimal to
    do this.  This document defines a new field in the PIM Join message
    that allows it to use TLVs, hereby called the attribute field.  The
    content and purpose of this attribute field is outside the scope of
    this document, only the generic encoding format is described here.


2.  Use of the Attribute Field in Join Messages

2.1.  Attribute join

    Attribute fields are defined similar to the PIM source encoding type
    as defined in [I-D.ietf-pim-sm-v2-new].  A source address without any
    additional TLV's should be processed identically to a source address
    in the default source encoding.

    Multiple TLV's from the same or different type are permitted in a
    single source address in any order.

2.2.  Transitive attributes

    It may be desired to have routers that understand the generic
    attribute format, forward the attributes regardless if they
    understand the TLV's encoded in the attribute not.  For this the
    first bit in the Type field is reserved.  If this bit is set then the
    TLV is forwarded upstream in case the router does not understand that
    type.

2.3.  Attribute Hello Option

    A new PIM source type has been defined to include the Attribute
    field.  This source type is included in a normal PIM Join.  Each
    router on a connected network needs to be able to understand and
    parse the Join message.  Therefore we include a new PIM hello option
    to advertise our capability to parse and process the new source type.
    We can only send a PIM Join which includes an attribute if ALL
    routers on the network support the new option.  (Even a router which
    is not the upstream neighbor must be able parse the packet in order
    to do Join suppression or overriding.)  Option value TBD.

    Having the attribute hello option does not guarantee that all
    neighbors understand all possible individual attributes.  As there's
    no immediate way to act on a neighbor's incapability to process
    certain attribute types, it is not desired to have a hello option for
    each possible attribute type.



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2.4.  Conflicting Attributes

    It's possible that a router receives conflicting attribute
    information from different downstream routers.  See Figure 2.

        ( Edge A1 )            ( Edge B1 )---- [R1]
       /           \          /
      /             \        /
    [S]              ( Core )
      \             /        \
       \           /          \
        ( Edge A2 )            ( Edge B2 )---- [R2]


         Figure 2

    There are 2 receivers for the same group connected to Edge B1 and B2.
    Suppose that edge router B1 prefers A1 as the exit point and B2
    prefers A2 as exit point to reach the source S. If both Edge B1 and
    B2 send a Join including an attribute to prefer their exit router in
    the network and they cross the same core router, the core router will
    get conflicting attribute information for the source.  If this
    happens we use the Attribute from the PIM adjacency with the
    numerically smallest IP address.  The Attributes from other sending
    routers may be kept around in case the best Attribute gets pruned or
    expires, we are able to immediately use the second best Attribute and
    converge quickly without waiting for the next periodic update.  If a
    TLV has its own definition for conflict resolution it is preferred
    over the conflict resolution above.

2.5.  Attribute Convergence

    An Attribute is included in a PIM Join message together with the
    source information.  If the Attribute for this source is changed, we
    trigger a new PIM Join message to the upstream router.  This causes
    the new Attribute to be propagated.  This new Attribute implicitly
    removes the old Attribute upstream.  If processing the new Attribute
    results in a change in the distribution tree, a PIM Prune message may
    be sent.  This PIM Prune does not need to carry any Attribute, the
    sender of the prune and the source and group information is enough to
    identify the entry.  The attribute information is removed immediately
    and possibly a new attribute is chosen from the database if
    available.

2.6.  Multiple Attributes

    A PIM Join can contain multiple Attributes.  The Attributes are
    encoded as TLVs associated with a new PIM source type in the PIM



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    message.  When a PIM Join with multiple Attributes is received, the
    first Attribute is processed, and the action taken depends upon the
    Attribute type.  This may or may not result in the processing of the
    next Attribute.  Attributes not processed are passed upstream
    unchanged.


3.  PIM Attribute packet format

3.1.  PIM Join packet format

    There is no space in the default PIM source encoding to include a
    Attribute field.  Therefore we introduce a new source encoding type.
    The attributes are formatted as TLV's.  The new Encoded source
    address looks like this:

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Addr Family   | Encoding Type | Rsrvd   |S|W|R|  Mask Len     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Source Address                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |F|S|  Type     | Length        | Value
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
    |F|S|  Type     | Length        | Value
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
            .                    .                     .
            .                    .                     .

    F bit, Forward Unknown TLV.  If this bit is set the TLV is forwarded
    regardless if the router understands the Type.

    S bit, Bottom of Stack.  If this bit is set then this is the last TLV
    in the stack.

    Type field of the TLV is 6 bits.

    Length field of the TLV is 1 byte.

    The other fields are the same as described in the PIM spec.
    [I-D.ietf-pim-sm-v2-new].

    The source TLV encoding type: TBD.







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3.2.  PIM Attribute Hello option

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      OptionType = XX          |      OptionLength = 0         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Option type: TBD.


4.  Acknowledgments

    The authors would like to thank James Lingard for his comments on
    this topic.


5.  References

5.1.  Normative References

    [I-D.ietf-pim-sm-v2-new]
               Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
               "Protocol Independent Multicast - Sparse Mode PIM-SM):
               Protocol Specification  (Revised)",
               draft-ietf-pim-sm-v2-new-11 (work in progress),
               October 2004.

5.2.  Informative References
























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Authors' Addresses

    Arjen Boers
    Cisco Systems, Inc.
    Avda. Diagonal, 682
    Barcelona  08034
    Spain

    Email: aboers@cisco.com


    IJsbrand Wijnands
    Cisco Systems, Inc.
    De kleetlaan 6a
    Diegem  1831
    Belgium

    Email: ice@cisco.com


    Eric Rosen
    Cisco Systems, Inc.
    1414 Massachusetts Avenue
    Boxborough, Ma  01719

    Email: erosen@cisco.com

























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