wdiff rfc6807.original rfc6807.txt

Network Working Group Dino
Internet Engineering Task Force (IETF) D. Farinacci
Internet-Draft Greg
Request for Comments: 6807 G. Shepherd
Intended status:
Category: Experimental Stig S. Venaas
Expires: April 7, 2013
ISSN: 2070-1721 Cisco Systems
Yiqun
Y. Cai
Microsoft
October 4,
November 2012

Population Count Extensions to PIM
draft-ietf-pim-pop-count-07.txt Protocol Independent Multicast (PIM)

Abstract

This specification defines a method for providing multicast
distribution-tree accounting data. Simple extensions to the PIM Protocol
Independent Multicast (PIM) protocol allow a rough approximation of
tree-based data in a scalable fashion.

Status of this This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

Internet-Drafts are working documents
evaluation.

This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a maximum candidate for any level of six months
Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on April 7, 2013.
http://www.rfc-editor.org/info/rfc6807.

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. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Pop-Count-Supported Hello Option . . . . . . . . . . . . . . . 5 4
3. New Pop-Count Join Attribute Format . . . . . . . . . . . . . 6 5
3.1. Options . . . . . . . . . . . . . . . . . . . . . . . . . 9 8
3.1.1. Link Speed Encoding . . . . . . . . . . . . . . . . . 10
3.2. Example message layouts Message Layouts . . . . . . . . . . . . . . . . . 11 10
4. How to use Use Pop-Count Encoding . . . . . . . . . . . . . . . . 13 11
5. Implementation Approaches . . . . . . . . . . . . . . . . . . 14 12
6. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 14
10.1. Normative References . . . . . . . . . . . . . . . . . . . 19 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 14

1. Introduction

This document specifies a mechanism to convey accounting information
using the PIM Protocol Independent Multicast (PIM) protocol [RFC4601]
[RFC5015]. Putting the mechanism in PIM allows efficient
distribution and maintenance of such accounting information.
Previous mechanisms require data to be correlated from multiple
router sources.

This mechanism allows a single router to be queried to obtain
accounting and statistic information for a multicast distribution
tree as a whole or any distribution sub-tree downstream from a
queried router. The amount of information is fixed and does not
increase as multicast membership, tree diameter, or branching
increase.
increases.

The sort of accounting data this specification provides, on a per
multicast route per-
multicast-route basis, are:

1. The number of branches in a distribution tree.

2. The membership type of the distribution tree, that is is, Source-
Specific Multicast (SSM) or Any-Source Multicast (ASM).

3. Routing domain and time zone boundary information.

4. On-tree node and tree diameter counters.

5. Effective MTU and bandwidth.

This document defines a new PIM Join Attribute type [RFC5384] to for the
Join/Prune message as well as a new Hello option. The mechanism is
applicable to IPv4 and IPv6 multicast.

This is a new extension to PIM, and it is not completely understood
what impact collecting information using PIM would have on the
operation of PIM. This is an entirely new concept. Many PIM
features (including the core protocols) were first introduced as in
Experimental RFCs, and it seems appropriate to advance this work as
Experimental. Reports of implementation and deployment across whole
distribution trees or within sub-trees (see Section 6) will enable an
assessment of the desirability and stability of this specification.
The PIM working group Working Group will then consider whether to move this work to
the Standards Track.

This document does not specify how an administrator or user can
access this information. It is expected that an implementation may
have a command line command-line interface or other ways of requesting and
displaying this information. As this is currently an Experimental
document, defining a MIB module has not been considered. If the PIM
working group
Working Group finds that this should move on to Standards Track, a
MIB module should be considered.

1.1. Requirements Notation

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].

1.2. Terminology

This section defines the terms used in this document.

Multicast Route: A An (S,G) or (*,G) entry regardless if of whether the
route is in ASM, SSM, or Bidir BIDIR mode of operation.

Stub Link: A link with members joined to the group via IGMP or
Multicast Listener Discovery (MLD) (MLD).

Transit Link: A link put in the oif-list (outgoing interface list)
for a multicast route because it was joined by PIM routers.

Note that a link can be both a Stub Link and a Transit Link at the
same time.

2. Pop-Count-Supported Hello Option

A PIM router indicates that it supports the mechanism specified in
this document by including the Pop-Count-Supported Hello option in
its PIM Hello message. Note that it also needs to include the Join-
Attribute Hello option as specified in [RFC5384]. The format of the
Pop-Count-Supported Hello option is defined to be:

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 | OptionLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

OptionType = TBD1, 29, OptionLength = 0. Note that there is no option
value included. In order to allow future updates of this
specification that may include an option value, implementations of
this document MUST accept and process this option also even if the length
is non-zero. Implementations of this specification MUST accept and
process the option ignoring any option value that may be included.

3. New Pop-Count Join Attribute Format

When a PIM router supports this mechanism and has determined from a
received Hello, Hello that the neighbor supports this mechanism, and also
that all the neighbors on the interface support the use of join
attributes, it will send Join/Prune messages that MAY include a Pop-
Count Join Attribute. The mechanism to process a PIM Join Attribute
is described in [RFC5384]. The format of the new attribute is
specified in the following.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type Attr_Type | Length | Effective MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Options Bitmap |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options |
. . .
. . .
. . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The above format is used only for entries in the join-list section of
the Join/Prune message.

F bit: 0 Non-Transitive Attribute. (Non-Transitive Attribute).

E bit: As specified by [RFC5384].

Attr Type: TBD2.

Attr_Type: 3.

Length: The minimum length is 6.

Effective MTU: This contains the minimum MTU for any link in the
oif-list. The sender of a Join/Prune message takes the minimum
value for the MTU (in bytes) from each link in the oif-list. If
this value is less than the value stored for the multicast route
(the one received from downstream joiners) joiners), then the value should
be reset and sent in a Join/Prune message. Otherwise, the value
should remain unchanged.

This provides one to obtain the MTU supported by multicast distribution tree
when examined at the first-hop router(s) or for sub-tree for any
router on the distribution tree.

Flags: The flags field has the following format:

0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unalloc/Reserved |P|a|t|A|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unallocated/Reserved Flags: The flags which that are currently not
defined. If a new flag is defined and used by a new
implementation, an old implementation should preserve the bit
settings. This means that a router MUST preserve the settings
of all Unallocated/Reserved Flags in PIM Join messages received
from downstream routers in any PIM Join sent upstream.

S flag: If This flag is set if an IGMPv3 or MLDv2 report with an
INCLUDE Mode mode group record was received on any oif-list entry or
the bit was set from any PIM Join message. This bit should
only be cleared when the above becomes untrue.

A flag: If This flag is set if an IGMPv3 or MLDv2 report with an
EXCLUDE Mode mode group record, or an IGMPv1, IGMPv2, or MLDv1
report, was received on any oif-list entry or the bit was set
from any PIM Join message. This bit should only be cleared
when the above becomes untrue.

A combination of settings for these bits indicate:

A-flag S-flag

A flag S flag Description
------ ------ --------------------------------------
0 0 There are no members for the group group.
('Stub Oif-List Count' is 0)
0 1 All group members are using SSM SSM.
1 0 All group members are using ASM ASM.
1 1 A mixture of SSM and ASM group members members.

t flag: If This flag is set if there are any manually configured
tunnels on the distribution tree. This means any tunnel that
is not an auto-tunnel. If a manually configured tunnel is in
the oif-list, a router should set sets this bit in its Join/Prune
messages. Otherwise, it propagates the bit setting from
downstream joiners.

a flag: If This flag is set if there are any auto-tunnels on the
distribution tree. If an auto-tunnel is in the oif-list, a
router should set sets this bit in its Join/Prune messages. Otherwise, it
propagates the bit setting from downstream joiners. An example
of an auto-
tunnel auto-tunnel is an a tunnel setup set up by the AMT
[I-D.ietf-mboned-auto-multicast] Automatic Multicast
Tunneling [AMT] protocol.

P flag: This flag is set by a router if all downstream routers
support this specification. That is, they are all PIM pop-
count Pop-
Count capable. If a downstream router does not support this
specification
specification, it MUST be cleared. This allows one to tell if
the entire sub-tree is completely accounting capable.

Options Bitmap: This is a bitmap that shows which options are
present. The format of the bitmap is as follows:

0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|s|m|M|d|n|D|z| Unalloc/Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Each one of the bits T, s, m, M, d, n, D and z is associated with
one option, where the option is included if and only if the
respective bit is set. Included options MUST be in the same order
as these bits are listed. The bits denote the following options:

bit Option
----- ------------------------
T Transit Oif-List Count
s Stub Oif-List Count
m Minimum Speed Link
M Maximum Speed Link
d Domain Count
n Node Count
D Diameter Count
z TZ Count

See Section 3.1 for details on the different options. The
unallocated bits are reserved. Any unknown bits MUST be set to 0
when a message is sent, and treated as 0 (ignored) when received.
This means that unknown options which that are denoted by unknown bits
are ignored.

By using this bitmap we can specify at most 16 options. If there
becomes a need for more than 16 options, one can define a new
option that contains a bitmap, which bitmap that can then be used to specify
which further options are present. The last bit in the current
bitmap could be used for that option. The However, the exact
definition of this is however left for future documents.

Options: This field contains options. Which options are present
are is
determined by the flag bits. As new flags and options may be
defined in the future, any unknown/reserved flags MUST be ignored,
and any additional trailing options MUST be ignored. See
Section 3.1 for details on the options defined in this document.

3.1. Options

There are several options defined in this document. For each option,
there is also a related flag that shows whether the option is
present. See the Options Bitmap above for a list of the options and
their respective bits. Each option has a fixed size. Note that
there is are no alignment requirements for the options, so an
implementation cannot assume they are aligned.

Transit Oif-List Count: This is filled in by a router sending a
Join/Prune message indicating the number of transit links on the
multicast distribution tree. The value is the number of oifs
(outgoing interfaces) for the multicast route that have been
joined by PIM plus the sum of the values advertised by each of the
downstream PIM routers that have joined on this oif. Length is 4
octets.

Stub Oif-List Count: This is filled in by a router sending a Join/
Prune message indicating the number of stub links (links where
there are host members) on the multicast distribution tree. The
value is the number of of oifs for the multicast route that have been
joined by IGMP or MLD plus the sum of the values advertised by
each of the downstream PIM routers that have joined on this oif.
Length is 4 octets.

Minimum Speed Link: This contains the minimum bandwidth rate for any
link in the oif-list and is encoded as specified in Section 3.1.1.
The sender of a Join/Prune message takes the minimum value for
each link in the oif-list for the multicast route. If this value
is less than the value stored for the multicast route (the
smallest value received from downstream joiners) joiners), then the value
should be reset and sent in a Join/Prune message. Otherwise, the
value should remain unchanged. This This, together with the Maximum
Speed Link option option, provides a way to obtain the lowest lowest- and highest
speed link
highest-speed links for the multicast distribution tree. Length
is 2 octets.

Maximum Speed Link: This contains the maximum bandwidth rate for any
link in the oif-list and is encoded as specified in Section 3.1.1.
The sender of a Join/Prune message takes the maximum value for
each link in the oif-list for the multicast route. If this value
is greater than the value stored for the multicast route (the
largest value received from downstream joiners) joiners), then the value
should be reset and sent in a Join/Prune message. Otherwise, the
value should remain unchanged. This This, together with the Minimum
Speed Link option option, provides a way to obtain the lowest lowest- and highest speed link
highest-speed links for the multicast distribution tree. Length
is 2 octets.

Domain Count: This indicates the number of routing domains the
distribution tree traverses. A router should increment this value
if it is sending a Join/Prune message over a link which that traverses a
domain boundary. For this to work, an implementation needs a way
of knowing that a neighbor or an interface is in a different
domain. There is no standard way of doing this. Length is 1
octet.

Node Count: This indicates the number of routers on the distribution
tree. Each router will sum up all the Node Counts from all
joiners on all oifs and increment by 1 before including this value
in the Join/Prune message. Length is 1 octet.

Diameter Count: This indicates the longest length of any given
branch of the tree in router hops. Each router that sends a Join
increments the max value received by all downstream joiners by 1.
Length is 1 octet.

TZ Count: This indicates the number of timezones time zones the distribution
tree traverses. A router should increment this value if it is
sending a Join/Prune message over a link which that traverses a time
zone. This can be a configured link attribute attribute, or use using other
means to determine the timezone time zone is acceptable. Length is 1
octet.

3.1.1. Link Speed Encoding

The speed is encoded using 2 octets as follows:

0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exponent | Significand |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Using this format, the speed of the link is Significand * 10 ^
Exponent kbps. This allows specifying link speeds with up to 3
decimal digits precision and speeds from 1 kbps to 10 ^ 67 kbps. A
computed speed of 0 kbps means the link speed is < 1 kbps.

Here are some examples of how this is used:

Link Speed Exponent Significand
------------ ---------- -------------
500 kbps 0 500
500 kbps 2 5
155 Mbps 3 155
40 Gpbs 6 40
100 Gpbs 6 100
100 Gpbs 8 1

3.2. Example message layouts

We Message Layouts

Here, we will here give a few examples to illustrate the use of flags and
options.

A minimum size minimum-size message has no option flags set, set and 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type Attr_Type | Length = 6 | Effective MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unalloc/Reserved |P|a|t|A|S|0|0|0|0|0|0|0|0| Unalloc/Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A message containing all the options defined in this document would
look 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type Attr_Type | Length = 18 | Effective MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unalloc/Reserved |P|a|t|A|S|1|1|1|1|1|1|1|1| Unalloc/Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transit Oif-List Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stub Oif-List Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Speed Link | Maximum Speed Link |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Count | Node Count | Diameter Count| TZ Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A message containing only Stub Oif-List Count and Node Count would
look 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type Attr_Type | Length = 9 | Effective MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unalloc/Reserved |P|a|t|A|S|0|1|0|0|0|1|0|0| Unalloc/Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stub Oif-List Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node count |
+-+-+-+-+-+-+-+-+

4. How to use Use Pop-Count Encoding

A router supporting this mechanism MUST, unless administratively
disabled, include the PIM Join Attribute option in its PIM Hellos.
See [RFC5384] and [HELLO] "PIM-Hello Options" on [PIM-REG] for details.

It is RECOMMENDED that implementations allow for administrative
control of whether to make use of this mechanism. Implementations
MAY also allow further control of what information to store and send
upstream.

It is very important to note that any changes to the values
maintained by this mechanism MUST NOT trigger a new Join/Prune
message. Due to the periodic nature of PIM, the values can be
accurately obtained at 1 minute 1-minute intervals (or whatever Join/Prune
interval used).

When a router removes a link from an oif-list, it need needs to be able to
reevaluate the values that it will advertise upstream. This happens
when an oif-list entry is timed out or a Prune is received.

It is RECOMMENDED that the Join Attribute defined in this document be
used only for entries in the join-list part of the Join/Prune
message. If the attribute is used in the prune-list, an
implementation MUST ignore it and process the Prune as if the
attribute was were not present.

It is also RECOMMENDED that join suppression be disabled on a LAN
when Pop-Count is used.

It is RECOMMENDED that that, when triggered Join/Prune messages are sent
by a downstream router, that the accounting information not be included in
the message. This way way, when convergence is important, avoiding the
processing time to build an accounting record in a downstream router
and processing time to parse the message in the upstream router will
help reduce convergence time. An If an upstream router SHOULD NOT
interpret receives a Join/Prune Join/
Prune message received with no accounting data data, it SHOULD NOT interpret the
message as a trigger to
mean clearing clear or resetting what reset the accounting data it has
cached.

5. Implementation Approaches

This section offers some non-normative suggestions for how pop-count Pop-Count
may be be implemented.

An implementation can decide how the accounting attributes are
maintained. The values can be stored as part of the multicast route
data structure by combining the local information it has with the
joined information on a per oif per-oif basis. So So, when it is time to send a
Join/Prune message, the values stored in the multicast route can be
copied to the message.

Or, an implementation could store the accounting values per oif and and,
when a Join/Prune message is sent, it can combine the oifs with its
local information. Then Then, the combined information can be copied to
the message.

When a downstream joiner stops joining, accounting values cached must
be evaluated. There are two approaches which that can be taken. One is to
keep values learned from each joiner joiner, so when the joiner goes away away,
the count/max/min values are known and the combined value can be
adjusted. The other approach is to set the value to 0 for the oif,
and then start accumulating new values as subsequent Joins are
received.

The same issue arises when an oif is removed from the oif-list.
Keeping per-oif values allows you to adjust the per-route values when
an oif goes away. Or, alternatively, a delay for reporting the new
set a values from the route can occur while all oif values are zeroed
(where accumulation of new values from subsequent Joins cause re-
population
repopulation of values and a new max/min/count can be reevaluated for
the route).

6. Caveats

This specification requires each router on a multicast distribution
tree to support this specification or else the accounting attributes
for the tree will not be known.

However, if there are is a contiguous set of routers downstream in the
distribution tree, they can maintain accounting information for the
sub-tree.

If there are is a set of contiguous routers supporting this specification
upstream on the multicast distribution tree, accounting information
will be available available, but it will not represent an accurate assessment
of the entire tree. Also, it will not be clear for how much of the
distribution tree the accounting information covers.

7. IANA Considerations

A new PIM Hello PIM-Hello Option type, 29, has been assigned temporarily. The
string TBD1 needs to be replaced with the permanently assigned value.
See [HELLO] for details. by IANA. Although
the length is specified as 0 in this specifications, specification, non-zero length
is allowed, so IANA should list has listed the length as being variable.

A new PIM Join Attribute type needs to be assigned. The string TBD2
needs to be replaced with the type, 3, has been assigned value. by IANA.

8. Security Considerations

The use of this specification requires some additional processing of
PIM Join/Prune messages. However, the additional amount of
processing is fairly limited, so this is not believed to be a
significant concern.

The use of this mechanism includes information like the number of
receivers. This information is assumed to not be of a sensitive
nature. If an operator has concerns about revealing this information
to upstream routers, routers or other routers/hosts that may potentially
inspect this information, there should be a way to disable the
mechanism, or alternatively
mechanism or, alternatively, more detailed control of what
information to include.

9. Acknowledgments

The authors would like to thank John Zwiebel, Amit Jain, and Clayton
Wagar for their review comments on the initial versions of this
document. Adrian Farrel did a detailed review of the document and
proposed textual changes that have been incorporated. Further review
and comments were provided by Thomas Morin and Zhaohui (Jeffrey)
Zhang.

10. References

10.1. 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.

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

[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, November 2008.

10.2. Informative References

[HELLO] IANA, "PIM-Hello Options",
<http://www.iana.org/assignments/pim-parameters>.

[I-D.ietf-mboned-auto-multicast]

[AMT] Bumgardner, G., "Automatic Multicast Tunneling",
draft-ietf-mboned-auto-multicast-14 (work Work
in progress), Progress, June 2012.

[PIM-REG] IANA, "Protocol Independent Multicast (PIM) Parameters",
<http://www.iana.org/assignments/pim-parameters>.

Authors' Addresses

Dino Farinacci
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA

Email:

EMail: dino@cisco.com

Greg Shepherd
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA

Email:

EMail: gjshep@gmail.com

Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA

Email:

EMail: stig@cisco.com

Yiqun Cai
Microsoft
1065 La Avenida
Mountain View, CA 94043
USA

Email:

EMail: yiqunc@microsoft.com