PIM WG Arjen Boers
Internet Draft IJsbrand Wijnands
Intended Status: Proposed Standard Eric C. Rosen
Expires: December 30, 2008 Cisco Systems, Inc.
June 30, 2008
The PIM Join Attribute Format
draft-ietf-pim-join-attributes-04.txt
Status of this Memo
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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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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 to any PIM neighbor that has not
included this option in its Hellos.
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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
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. Intellectual Property
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Boers, et al. [Page 12]
