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Versions: 00 01 02 03 04 05 06 RFC 5384

PIM WG                                                       Arjen Boers
Internet Draft                                         IJsbrand Wijnands
Intended Status: Proposed Standard                         Eric C. Rosen
Expires: January 28, 2009                            Cisco Systems, Inc.

                                                           July 28, 2008


                     The PIM Join Attribute Format


                 draft-ietf-pim-join-attributes-05.txt

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Abstract

   A Protocol Independent Multicast (PIM) Join message sent by a given
   node identifies one or more multicast distribution trees that that
   node wishes to join.  Each tree is identified by a multicast group
   address and a source address, which is possibly a "wild card".  Under
   certain conditions it can be useful, when joining a tree, to specify
   additional information related to the construction of the tree.
   However, there is up to now no way to do so.  This document describes
   a modification of the Join message that allows a node to associate
   attributes with a particular tree.  The attributes are encoded in
   Type-Length-Value format.



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Internet Draft    draft-ietf-pim-join-attributes-05.txt        July 2008


Table of Contents

 1          Specification of requirements  .........................   2
 2          Introduction  ..........................................   3
 3          Use of Join Attributes  ................................   4
 3.1        Sending Join Attributes  ...............................   4
 3.2        The Join Attribute Option in the PIM Hello  ............   4
 3.3        Receiving Join Attributes  .............................   5
 3.3.1      General Considerations  ................................   5
 3.3.2      Transitive and Non-Transitive Attributes  ..............   5
 3.3.3      Conflicting Attributes  ................................   6
 3.3.4      Attribute Change  ......................................   7
 3.4        PIM Attribute Packet Format  ...........................   8
 3.4.1      PIM Join Packet Format  ................................   8
 3.4.2      PIM Join Attribute Hello Option  .......................   9
 4          IANA Considerations  ...................................   9
 5          Security Considerations  ...............................  10
 6          Acknowledgments  .......................................  10
 7          Authors' Addresses  ....................................  10
 8          Normative References  ..................................  11
 9          Informative References  ................................  11
10          Full Copyright Statement  ..............................  11
11          Intellectual Property  .................................  11






1. Specification of requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].













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2. Introduction

   A Protocol Independent Multicast (PIM) Join message sent by a given
   node may identify one or more multicast distribution trees that that
   node wishes to join.  Each tree is identified by a multicast group
   address and a source address, which is possibly a "wild card".  Under
   certain conditions it can be useful, when joining a tree, to specify
   additional information related to the construction of the tree.
   However, there is up to now no way to do so.  This document describes
   a modification of the Join message that allows a node to associate an
   attribute, encoded in  Type-Length-Value (TLV) format, with a
   particular tree that it wishes to join.  These attributes are known
   as "PIM Join Attributes".

   In the PIM Join message, the Source Address is identified by being
   encoded as an "Encoded-Source Address" ([RFC4601], section 4.9.1).
   Each Encoded-Source Address occurs in the context of a particular
   group address, represented as an "Encoded-Group Address".  Together
   the Encoded-Source Address and the Encoded-Group Address identify a
   multicast distribution tree.  The Encoded-Source Address contains an
   "encoding type" field.  The only value defined in [RFC4601] is 0.
   This specification is the first to assign another encoding type
   value.

   In order to associate TLVs with a particular tree, this specification
   defines a new encoding type for the Encoded-Source address, type 1.
   When type 1 is used, the Encoded-Source Address may contain a
   sequence of "Join Attributes", each of which is encoded as a TLV.
   Then the type 1 Encoded-Source Address, in the context of the
   associated Encoded-Group Address, identifies a multicast distribution
   tree, and also specifies (via the Join Attribute TLVs) the attributes
   that apply to the tree.  Apart from the fact that the type 1 Encoded-
   Source Address may contain Join Attributes, it is otherwise identical
   to the type 0 Encoded-Source Address.

   This document does not contain the specification for any particular
   Join Attribute.  It specifies how Join Attributes are to be encoded
   into the Join messages, and it specifies generic procedures that are
   common to all Join Attributes. The content and purpose of any
   particular Join Attribute is outside the scope of this document.

   The use of Join Attributes in "Dense Mode" PIM is not considered.









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3. Use of Join Attributes

3.1. Sending Join Attributes

   Join Attributes are encoded as TLVs into the Encoded-Source Address
   field of a PIM Join message, as specified in section 3.3.1 below.
   Each attribute applies to same multicast distribution tree that is
   identified by the combination of the Encoded-Source Address and the
   associated Encoded-Group address.  The multicast distribution tree
   may be either a source-specific tree or a shared tree.

   The encoding of the "source address" field within the Encoded-Source
   Address is exactly the same for a type 1 Encoded-Source Address as
   for a type 0 Encoded-Source Address, as specified in [RFC4601].

   A type 1 Encoded-Source Address MUST contain at least one Join
   Attribute.  The way to specify that there are no Join Attributes for
   a particular tree is to use the type 0 Encoded-Source Address.

   Multiple Join Attributes of the same type or of different types may
   occur within a single Encoded-Source Address.  This specification
   does not require all attributes of a given type to occur
   contiguously.  There is no header field that specifies the number of
   attributes; rather the last attribute is specially marked as such.

   Any PIM router that does not understand the type 1 Encoded-Source
   Address will not be able to process a PIM Join message that contains
   it.  Further, if the use of any particular Join Attribute affects the
   construction of the multicast distribution tree, the tree may not be
   formed correctly unless the attribute is understood by all PIM
   routers that receive it.  As a consequence, attributes are only
   useful within a single administrative domain (or perhaps a small set
   of contiguous, cooperating administrative domains) where it can be
   determined apriori that all deployed PIM routers understand the type
   1 Encoded-Source address, as well as whatever specific attributes are
   in use.


3.2. The Join Attribute Option in the PIM Hello

   To ensure that a type 1 Encoded-Source Address is not sent to a PIM
   neighbor that does not understand this encoding, a new PIM Hello
   option, the "Join Attribute" option, is defined.  This option must be
   included in the PIM Hello's of any PIM router that is willing to
   receive type 1 Encoded-Source Address.  A PIM router MUST NOT send a
   type 1 Encoded-Source Address out any interface on which there is a
   PIM neighbor that has not included this option in its Hellos.  (Even
   a router which is not the upstream neighbor must be able parse the



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   packet in order to do Join suppression or overriding.)

   Note that a PIM router that sends the "Join Attribute" Hello option
   does not necessarily understand every possible attribute type.  As
   there is no immediate way to act on a neighbor's inability to process
   certain attribute types, it is not desired to have a hello option for
   each possible attribute type.


3.3. Receiving Join Attributes

3.3.1. General Considerations

   A PIM router that receives a type 1 Encoded-Source Address MUST
   process the first attribute in it.  The result of processing that
   attribute may affect the following:

     - the construction of the associated multicast distribution tree

     - the processing of subsequent attributes of the same type that
       also occur in the type 1 Encoded-Source Address

     - the forwarding (or not) of the attribute itself and/or
       subsequently occurring attributes of the same type.

   If multiple types of attribute occur in a type 1 Encoded-Source
   Address, the first attribute of each type MUST be processed.


3.3.2. Transitive and Non-Transitive Attributes

   If a PIM router understands a particular attribute type, the
   attribute is processed as specified above.

   If a PIM router does not understand the type of a particular
   attribute, the PIM router either forwards that attribute or discards
   it, depending upon the setting of the attribute's F-bit.  If the F-
   bit is set, then the router MUST forward the attribute; if the F-bit
   is clear, then the router MUST discard it.

   If one or more non-transitive attributes are discarded, the rest of
   the Join Attributes (if any) are still forwarded.  If there are no
   Join Attributes left to forward, a Join with a type 0 Encoded-Source
   Address field would be forwarded.







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3.3.3. Conflicting Attributes

   It is possible that a router receives conflicting attribute
   information from different downstream routers. Conflicts only occur
   with attributes of the same type.



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


        Figure 2



   As an example, consider Figure 2, and suppose a join attribute is
   used to indicate a choice of 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. In the
   case of IPv6, the link local address will be used. When two neighbors
   have the same IP address, either for IPv4 or IPv6, the interface
   index must be used as a tie breaker.  The attributes from other
   sending routers MAY be remembered; then if 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.

   When a particular attribute type is specified, the specification MAY
   include a conflict resolution procedure specific to that type.  If
   so, that conflict resolution procedure would be used instead of the
   described in this section.

   The conflict resolution procedure described in this section is also
   used by a router if there are conflicting transitive attributes that
   the router does not understand.





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3.3.4. Attribute Change

   A PIM router may decide to change the set of attributes it has
   associated with a given multicast distribution tree.  This can happen
   if one of its downstream neighbors on the tree has changed the set of
   attributes.  It can also happen as a result of processing the
   attributes.  It can also happen for reasons outside the scope of this
   specification (such as a change in configuration.)

   If a PIM router needs to change the set of attributes for a given
   tree, but does not change its upstream neighbor for that tree, it
   MUST send a new Join for that tree, specifying the new set of
   attributes.  If the new set of attributes is the null set, the type 0
   Encoded-Source format MUST be used.

   If a PIM router needs to change the set of attributes for a given
   tree, and as a result changes its upstream neighbor for that tree, it
   sends a Prune to the old upstream neighbor.  The Prune does not need
   to carry any attributes.

   When a PIM router receives a Join for a given tree, and the Join does
   not contain exactly the same set of attributes as the prior Join, the
   set of attributes in the new Join becomes the entire new set of
   attributes.  No attribute information from the prior Join is
   retained.  There is no way to advertise incremental changes to the
   set of attributes; any attributes that are no longer present are
   considered to have been withdrawn.  If, as the result of receiving a
   Join, a PIM router determines that the set of attributes has changed,
   it will need to send a new Join upstream, with the new set of
   attributes.  (Of course, the procedures for resolving attribute
   conflicts may need to be applied first.)

   When a PIM router R1 receives a Prune for a given tree from a given
   downstream neighbor R2, where R2 had previously sent attributes
   applying to that tree, those attributes are considered to have been
   withdrawn.  Depending on the attributes that R1 has received from its
   other downstream neighbors (if any) on the tree, R1 may determine
   that the set of attributes applying to the tree has changed, in which
   case it needs to send a new Join, with the new attribute set, to its
   upstream neighbor on the tree.











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3.4. PIM Attribute Packet Format

3.4.1. 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|E| Attr Type | Length        | Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
   |F|E| Attr_Type | Length        | Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
        .                    .                     .
        .                    .                     .


     - Encoding Type: 1

     - F bit, Transitive Attribute

       If this bit is set, the attribute is a transitive attribute;
       otherwise it is a non-transitive attribute.  See section 3.3.2.

     - E bit, End of Attributes.  If this bit is set then this is the
       last Join Attribute appearing in this Encoded-Source Address
       field.

     - "Attr_Type", a 6-bit field identifying the type of the Attribute.

     - Length field, a 1 octet field specifying the length in octets of
       the value field.

   The other fields are the same as described in [RFC4601].








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3.4.2. PIM Join Attribute Hello Option

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      OptionType = 26           |      OptionLength = 0        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option type: 26.




4. IANA Considerations

   A new IANA registry is needed for "PIM Join Attribute Types".  These
   are values of the "Attr_Type" field depicted in section 3.3.1.
   Assignments are to be made according to the policy "IETF Review" as
   defined in [RFC5226].

   The PIM Hello Option value 26 should be assigned by IANA to the "Join
   Attribute" option, with this document as the reference. [Assuming
   that 26 is still available.]

   [RFC4601] should have, but did not, create a registry for the
   "Encoding Type" field of the Encoded-Source Address format defined
   therein.  IANA should set up a registry for this, referencing
   [RFC4601].  Assignments should be made according to the policy "IETF
   Review" as defined in [RFC5226].  Two encoding types should be
   defined:

     - The encoding type 0 should be allocated, defined as "native
       encoding for the address family", and [RFC4601] should be the
       reference.

     - The encoding type 1 should be allocated, defined as "native
       encoding for the address family, but with zero or more PIM Join
       Attributes present", and this document should be the reference.













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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 [RFC4601] apply here.  Additional security
   considerations may apply to specific attributes; if so, these will
   need to be documented in the specification of those attributes.

   Security considerations from [RFC5015] may apply as well.



6. Acknowledgments

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


7. Authors' Addresses

   Arjen Boers
   Cisco Systems, Inc.
   Avda. Diagnoal, 682
   Barcelona 08034

   E-mail: aboers@cisco.com



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

   E-mail: ice@cisco.com



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

   E-mail: erosen@cisco.com





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8. Normative References

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

   [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
   "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol
   Specification (Revised)", RFC 4601, August 2006.


9. Informative References

   [RFC5015] "Bidirectional Protocol Independent Multicast", M. Handley,
   I. Kouvelas, T. Speakman, L. Vicisano, RFC 5015, October 2007.

   [RFC5226] "Guidelines for Writing an IANA Considerations Section in
   RFCs", T. Narten, H. Alvestrand, RFC 5226, May 2008.



10. Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   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
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


11. Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.




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