Network Working Group Dino Farinacci
Internet-Draft Greg Shepherd
Intended status: Experimental Yiqun Cai
Expires: January 2, 2010 cisco Systems
July 1, 2009
Population Count Extensions to PIM
draft-ietf-pim-pop-count-01.txt
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Abstract
This specification defines a method for providing multicast
distribution-tree accounting data. Simple extensions to the PIM
protocol allow a rough approximation of tree-based data in a scalable
fashion.
Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. New Hello TLV Pop-Count Support . . . . . . . . . . . . . . . 6
4. New Pop-Count Join Attribute Format . . . . . . . . . . . . . 7
5. How to use Pop-Count Encoding . . . . . . . . . . . . . . . . 10
6. Implementation Approaches . . . . . . . . . . . . . . . . . . 11
7. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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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].
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2. Introduction
This draft proposes a mechanism to convey accounting information
using the 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 proposal 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.
The sort of accounting data this draft provides, on a per multicast
route basis, are:
1. The number of branches in a distribution tree.
2. The membership type of the distribution tree, that is SSM or ASM.
3. Routing domain and time zone boundary information.
4. On-tree node and tree diameter counters.
5. Effective MTU and bandwidth.
This draft adds a new PIM Join Attribute type [RFC5384] to the Join/
Prune message as well as a new Hello TLV. The mechanism is
applicable to IPv4 and IPv6 multicast.
2.1. Terminology
This section defines the terms used in this draft.
Multicast Route: A (S,G) or (*,G) entry regardless if the route is
in ASM, SSM, or Bidir mode of operation.
Stub Link: A link with only members joined to the group via IGMP or
MLD. Which means there are no PIM routers joining for the
multicast route on the link.
Transit Link: A link put in the oif-list for a multicast route
because it was joined by PIM routers only (no IGMP or MLD reports
were received on the link).
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Dual Link: Is a link in the oif-list which is has the attributes of
a Stub Link *and* Transit Link. That is, there are IGMP and MLD
members as well as PIM joiners for the multicast route on the
link.
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3. New Hello TLV Pop-Count Support
When a PIM router sends a Join/Prune message to a neighbor, it will
encode the data in a new PIM Join Attribute type (described in this
draft) when the PIM router determines the neighbor can support this
draft. If a PIM router supports this draft, it must send the Pop-
Count-Supported TLV. The format of the TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionValue |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OptionType = 27, OptionLength = 8, there is no OptionValue semantics
defined at this time but will be included for expandability and be
defined in future revisions of this draft. The format will look
like:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 27 | 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unallocated Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unallocated Flags: for now should be sent as 0 and ignored on
receipt. This field could be used to enable the use of future
flags in the Unallocated Flags field of the new Encoded-Source-
Address format defined below.
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4. New Pop-Count Join Attribute Format
When a PIM router supports this draft and has determined from a
received Hello, the neighbor supports this draft, it will send Join/
Prune messages that MAY include a Pop-Count attribute. The mechanism
to process PIM Join Attribute is described in [RFC5384]. The format
of the new attribute is described 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 | Length | Effective MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unallocated Flags (Reserved) |P|a|t|A|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Count | Node Count | Diameter Count| TZ Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transit Oif-List Count | Stub Oif-List Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Speed Link | Maximum Speed Link |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The above format is used only for entries in the join-list section of
the Join/Prune message.
F bit: 0 Non-Transitive Attribute.
E bit: As specified by [RFC5384].
Attr Type: 2.
Length: 16.
Effective MTU: this contains the minimum MTU for any link in the
oif-list. The sender of 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) then the value should
be reset and sent in 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.
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Unallocated Flags: The flags which are currently not defined. If a
new flag is defined and sent by a new implementation, an old
implementation should preserve the bit settings.
S flag: if an IGMPv3 or MLDv2 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 flag: if 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 Description
------ ------ -----------------------------------------
0 0 There are no members for the group
('Stub Oif-List Count' is 0)
0 1 All group members are only SSM capable
1 0 All group members are only ASM capable
1 1 There is a mixture of SSM and ASM capable
t flag: if there are any tunnels on the distribution tree. If a
tunnel is in the oif-list, a router should set this bit in it's
Join/Prune messages. Otherwise, it propagates the bit setting
from downstream joiners.
a flag: if there are any auto-tunnels on the distribution tree. If
an auto-tunnel is in the oif-list, a router should set this bit in
it's Join/Prune messages. Otherwise, it propagates the bit
setting from downstream joiners. An example of an auto-tunnel is
an tunnel setup by the AMT [AMT] protocol.
P flag: this flag remains set if all downstream routers support
this specification. That is, they are PIM pop-count capable.
This allows one to tell if the entire sub-tree is completely
accounting capable.
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 traverses
a domain boundary.
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.
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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.
TZ Count: this indicates the number of timezones the distribution
tree traverses. A router should increment this value if it is
sending a Join/Prune message over a link which traverses a time
zone. This can be a configured link attribute or use other means
to determine the timezone is acceptable.
Transit Oif-List Count: is filled in by a router sending a Join/
Prune message which is equal to the number of oifs for the
multicast route that has been joined by PIM only. This indicates
the transit branches on a multicast distribution tree (no members
on the links between this router and joining routers). This is
added to the value advertised by all downstream PIM routers that
have joined on this oif.
Stub Oif-List Count: is filled in by a router sending a Join/Prune
message which is equal to the number of oifs for the multicast
route that has been joined only by IGMP or MLD. This indicates
the links where there are host members for the multicast route.
This is added to the value advertised by all downstream PIM
routers that have joined on this oif.
Minimum Speed Link: this contains the minimum bandwidth rate (in
mbps) for any link in the oif-list. The sender of 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 one received from downstream joiners)
then the value should be reset and sent in Join/Prune message.
Otherwise, the value should remain unchanged. A value of 0 means
the link speed is < 1 mbps.
Maximum Speed Link: this contains the maximum bandwidth rate (in
mbps) for any link in the oif-list. The sender of 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 one received from downstream
joiners) then the value should be reset and sent in Join/Prune
message. Otherwise, the value should remain unchanged. A value
of 0 means the link speed is < 1 mbps.
This provides a way to obtain the lowest and highest speed link for
the multicast distribution tree.
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5. How to use Pop-Count Encoding
A router supporting this draft MUST include PIM Join Attribute TLV in
its PIM Hellos. See [RFC5384] and [HELLO] for detail.
It is very important to note that any changes to the values
maintained in this draft *must not* trigger a new Join/Prune message.
Due to the periodic nature of PIM, the values can be accurately
obtained at 1 minute intervals (or whatever Join/Prune interval
used).
When a router removes a link from an oif-list, it must 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 draft be
used for entries in the join-list part of the Join/Prune message. If
the new encoding is used in the prune-list or an Assert message, an
implementation must ignore them but still process the Prune as if it
was in the original encoding described in [RFC4601].
It is also recommended that join suppression be disabled on a LAN
when Pop-Count is used.
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6. Implementation Approaches
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 basis. 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
when a Join/Prune message is sent, it can combine the oifs with it's
local information. 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 can be taken. One is
to keep values learned from each joiner so when the joiner goes 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 of values and a new max/min/ count can be reevaluated for
the route).
It is recommended that when triggered Join/Prune messages are sent by
a downstream router, that the accounting information not be included
in the message. This 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 upstream router should not
interpret a Join/Prune message received with no acccounting data to
mean clearing or resetting what accounting data it has cached.
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7. Caveats
This draft requires each router on a multicast distribution tree to
support this draft or else the accounting attributes for the tree
will not be known.
However, if there are a contiguous set of routers downstream in the
distribution tree, they can maintain accounting information for the
sub-tree.
If there are a set of contiguous routers supporting this draft
upstream on the multicast distribution tree, accounting information
will be 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.
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8. IANA Considerations
A new PIM Hello Option type needs to be assigned. 29 is proposed in
this draft.
A new PIM Join Attribute type needs to be assigned. 2 is proposed in
this draft.
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9. Security Considerations
There are no security considerations for this design other than what
is already in the main PIM specification [RFC4601].
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10. Acknowledgments
The authors would like to thank John Zwiebel, Amit Jain, and Clayton
Wagar for their review comments on the initial versions of this
draft.
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11. References
11.1. 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.
11.2. Informative References
[AFI] IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
NUMBERS http://www.iana.org/numbers.html, February 2007.
[AMT] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
Pusateri, "Automatic IP Multicast Without Explicit
Tunnels (AMT)", draft-ietf-mboned-auto-multicast-08.txt
(work in progress), October 2007.
[HELLO] IANA, "PIM Hello Options", PIM-HELLO-OPTIONS per
RFC4601 http://www.iana.org/assignments/pim-hello-options,
March 2007.
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Authors' Addresses
Dino Farinacci
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: dino@cisco.com
Greg Shepherd
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: shep@cisco.com
Yiqun Cai
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: ycai@cisco.com
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