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Network Working Group A. Boers Request for Comments: 5384 I. Wijnands Category: Standards Track E. Rosen

                                                   Cisco Systems, Inc.
                                                         November 2008

             The Protocol Independent Multicast (PIM)
                       Join Attribute Format

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (c) 2008 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.

Abstract

 A "Protocol Independent Multicast - Sparse Mode" 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 the combination
 of a multicast group address and a source address (where the source
 address 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 has been no
 way to do so until now.  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.

Boers, et al. Standards Track [Page 1] RFC 5384 PIM Join Attribute November 2008

Table of Contents

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

1. Introduction

 In the protocol known as "Protocol Independent Multicast - Sparse
 Mode" [RFC4601] (henceforth referred to as "PIM"), a 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 the
 combination of a multicast group address and a source address (where
 the source address 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 has been no way to do so until now.  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.

Boers, et al. Standards Track [Page 2] RFC 5384 PIM Join Attribute November 2008

 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 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 "Protocol Independent Multicast - Dense
 Mode" [RFC3973] is not considered.

2. 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].

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 3.4.1 below.
 Each attribute applies to the 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, 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.

Boers, et al. Standards Track [Page 3] RFC 5384 PIM Join Attribute November 2008

 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 a priori 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 Hellos 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 that is not the upstream neighbor must be able parse the
 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
 examine all the attributes in the order in which they appear.

 The specification for a given attribute type MUST specify the
 procedure to apply if there are multiple instances of that attribute
 type.

Boers, et al. Standards Track [Page 4] RFC 5384 PIM Join Attribute November 2008

 Processing an attribute may affect the following:

the construction of the associated multicast distribution tree,

the processing of other attributes of the same type that also occur

in the type 1 Encoded-Source Address, and

the forwarding (or not) of the attribute itself and/or other

attributes of the same type that also occur in the type 1 Encoded-

   Source Address.

 If the processing of a received attribute has any effect on the
 construction of the multicast distribution tree or on the set of
 attributes that are forwarded up the tree, then state MUST be
 maintained associating the received attribute with the adjacency or
 adjacencies from which it was received.

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 MUST be forwarded.

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 1

Boers, et al. Standards Track [Page 5] RFC 5384 PIM Join Attribute November 2008

 As an example, consider Figure 1 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 and B2 prefers A2 as exit points 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; that way, if the adjacency that supplied the selected
 attribute gets pruned or expires, we are able to immediately use the
 attribute that was sent by the adjacency that is next in the order of
 preference.  This enables us to 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 MUST be used instead of the
 procedure described in this section.

 It is possible that a router will receive, from two different
 adjacencies, transitive attributes of a given type.  If the router
 does not understand attributes of that type and if the two
 adjacencies have not sent the exact same set of attributes of that
 type, then the conflict resolution procedure described in this
 section MUST be applied to those attributes.  Two adjacencies are
 said to have sent the exact same set of attributes of a given type if
 they have sent the same number of instances of that attribute and if
 corresponding instances are byte-for-byte identical.

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.

Boers, et al. Standards Track [Page 6] RFC 5384 PIM Join Attribute November 2008

 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 that contains 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.

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 an
 attribute field.  Therefore we introduce a new source encoding type.
 The attributes are formatted as TLVs.  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
      .                    .                     .
      .                    .                     .

Boers, et al. Standards Track [Page 7] RFC 5384 PIM Join Attribute November 2008

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,

encoded as an unsigned binary integer, of the value field.

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

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 has been created for "PIM Join Attribute Types".
 These are values of the "Attr_Type" field depicted in section 3.4.1.
 Assignments are to be made according to the policy "IETF Review" as
 defined in [RFC5226].

 IANA has assigned the PIM Hello option value 26 to the "Join
 Attribute" option, with this document as the reference.

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

The encoding type 0 has been allocated, defined as "native encoding

for the address family", and [RFC4601] is the reference.

Boers, et al. Standards Track [Page 8] RFC 5384 PIM Join Attribute November 2008

The encoding type 1 has been allocated, defined as "native encoding

for the address family, but with zero or more PIM Join Attributes

   present", and this document is the reference.

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. Normative References

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

8. Informative References

 [RFC3973] Adams, A., Nicholas, J., and W. Siadak, "Protocol
           Independent Multicast - Dense Mode (PIM-DM): Protocol
           Specification (Revised)", RFC 3973, January 2005.

 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
           "Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
           RFC 5015, October 2007.

 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
           IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
           2008.

Boers, et al. Standards Track [Page 9] RFC 5384 PIM Join Attribute November 2008

Authors' Addresses

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

 EMail: aboers@cisco.com

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

 EMail: ice@cisco.com

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

 EMail: erosen@cisco.com

Boers, et al. Standards Track [Page 10]