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Versions: 00 01 02 03 04 05 06 RFC 5384

PIM WG                                                          A. Boers
Internet-Draft                                              IJ. Wijnands
Expires: September 2, 2006                                      E. Rosen
                                                     Cisco Systems, Inc.
                                                              march 2006


                 Format for using TLVs in PIM messages
                   draft-ietf-pim-join-attributes-01

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

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








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Table of Contents

   1.  Conventions used in this document . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Use of the Attribute Field in Join Messages . . . . . . . . . . 3
     3.1.  Attribute join  . . . . . . . . . . . . . . . . . . . . . . 3
     3.2.  Transitive attributes . . . . . . . . . . . . . . . . . . . 3
     3.3.  Attribute Hello Option  . . . . . . . . . . . . . . . . . . 3
     3.4.  Conflicting attributes  . . . . . . . . . . . . . . . . . . 4
     3.5.  Attribute Convergence . . . . . . . . . . . . . . . . . . . 4
     3.6.  Multiple attributes . . . . . . . . . . . . . . . . . . . . 5
     3.7.  Applicability of the attributes . . . . . . . . . . . . . . 5
     3.8.  PIM attribute packet format . . . . . . . . . . . . . . . . 5
       3.8.1.  PIM Join packet format  . . . . . . . . . . . . . . . . 5
       3.8.2.  PIM Attribute Hello option  . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9




























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1.  Conventions used in this document

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 and
   indicate requirement levels for compliant PIM-SM implementations.


2.  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.


3.  Use of the Attribute Field in Join Messages

3.1.  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.

3.2.  Transitive attributes

   It may be desired to have routers that understand the generic
   attribute format, forward the attributes regardless of whether 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
   router MUST forward the TLV upstream in case the router does not
   understand that type.  If this bit is not set the router MUST NOT
   forward the TLV upstream in the case the router does not understand
   that type.

3.3.  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.



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   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 to 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.

3.4.  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

   An example join attribute in this case is an exit router.  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.

3.5.  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



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   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.

3.6.  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
   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 that the router understands but are not
   processed MUST be passed upstream unchanged.

3.7.  Applicability of the attributes

   PIM Joins with attributes can be applied to both shared-trees rooted
   at a Rendezvous Point (RP) and shortest-path trees as described in
   [I-D.ietf-pim-sm-v2-new].

3.8.  PIM attribute packet format

3.8.1.  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 (Encoded-Source format)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |F|S|  Type     | Length        | Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
   |F|S|  Type     | Length        | Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
           .                    .                     .
           .                    .                     .

   F bit, Forward Unknown TLV.  If this bit is set the TLV is forwarded



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   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.

3.8.2.  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 = TBD          |      OptionLength = 0         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option type: TBD.


4.  IANA Considerations

   This document requires a new PIM Hello Option value and a new PIM
   Join Encoding type.


5.  Security Considerations

   Security of the join attribute is only guaranteed by the security of
   the PIM packet, so the security considerations for PIM join packets
   as described in PIM-SM [I-D.ietf-pim-sm-v2-new] apply here.


6.  Acknowledgments

   The authors would like to thank James Lingard, Bharat Joshi, Marshall
   Eubanks, Stig Venaas, Pekka Savola and Tom Pusateri for their input.


7.  References







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7.1.  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.

7.2.  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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