SSM in an AG context

Brian Chee chee at
Wed Oct 11 17:03:05 CDT 2000

Uh, one correction....VERY few routers (edge or otherwise) know how to talk
SSM!  IGMPv3 is NOT the only component....

I just did an SSM experiment at the Atlanta Networld+Interop show in the
I-Labs and at the moment the only relatively stable SSM load is on the Cisco
GSR(that we could find)....little expensive...more loads to follow per Cisco
engineering....Nortel seems to have some too, but we didn't obtain the code
in time for the show....I will try to do a small setup in my lab to continue
the SSM testing...

IGMPv3 stack patches are now available for BSD and Linux (linux confirmed,
BSD not) and rumor has it that Microsoft has one for Win2k....we did our
testing using an Ixia 1600 generator/analyzer.

We are still digging through our data...but it looks like you really only
need the SSM code on your edge routers....we did manage to send test SSM
packets from the PIM-SM/SSM cloud to the PIM-DM and DVMRP clouds....but this
was actually via MSDP/PIM-SM/MBGP....

Email me if you want a copy of the network map....

/brian chee

University of Hawaii at Manoa
Dept of Information & Computer Sciences
Advanced Network Computing Lab
Attn: Brian Chee
1680 East West Road, POST 311
Honolulu, HI  96822
808-956-5797 voice
----- Original Message -----
From: "Bill Nickless" <nickless at>
To: <ag-tech at>
Sent: Wednesday, October 11, 2000 11:35 AM
Subject: SSM in an AG context

> John Greenfield asked me some questions in the Waterfall Glenn Access Grid
> Room this afternoon.  These questions were related to Source Specific
> Multicast and IGMP Version 3.  I realized that I typed enough that I
> it in a permanent record: others may find this interesting too.  Comments
> welcome, as always.
> What is SSM?
> ============
> SSM -> Source Specific Multicast
> Currently, a receiver joins a multicast group but has no ability to
> specify a source. Multiple sources can exist and all data from them will
> received. SSM enables the selection of a particular source for multicast
> This prevents traffic from other sources for the same group from being
> forwarded to the host. SSM requires well-known sources and is most useful
> static applications.
> The preceding paragraph was a quote from
> in case you want to read more about it.  Apparently SSM is available in
> Cisco IOS 12.1(3)T.
> SSM requires IGMPv3 support in the edge routers and client hosts.  Current
> IGMPv2 allows the hosts to specify which groups they're interested in
> joining.   IGMPv3 extends this model to allow hosts to specify both the
> group AND the source.
> I've been led to believe that IGMPv3 support is available as patches to
> modern Linux kernels.  SSM is a new feature in IOS 12.1(3)T which
> is  available now on the router platforms we care about.  I have not heard
> anything about IGMPv3 availability on the Wintel (95/98/me/2k) platforms.
> Network implications
> ====================
> The only missing piece for SSM deployment right now is the IGMPv3 support,
> which lets a client specify both a sender and a group.  IGMPv2 (currently
> used) only lets a client express interest in a whole group.  Once the
> client requests traffic from a source on a group, standard PIM-SM and
> mechanisms are used to join the distribution tree.  Even the PIM-SM
> operation is simplified; the Rendezvous Point functionality goes away
> all distribution trees are source specific.
> MSDP is not required for SSM; it assumes the application (Access Grid in
> our case) knows about all active senders.  Again, the network no longer
> keeps track of all active senders in a given group.  Network Backbones
> Abilene should require no additional work to implement SSM, since modern
> inter-domain routing is all source-specific anyway.
> AG philosophical/planning implications
> ======================================
> In an AG context, that means three additional requirements: IGMPv3 support
> on all AG node machines.  VV support to keep track of all senders in real
> time.  Client software (vic/rat/&c) extensions to allow VV to feed in the
> addresses of active sources.
> The question of SSM revolves around how much we can depend on the
> application to know about all participants.
> My personal opinion is that SSM breaks the network support of our model of
> a virtual space.  Today a multicast group maps nicely into a virtual space
> abstraction. SSM is more of a point-to-manypoint distribution model; you
> have to build more infrastructure in order to regain that virtual space.
> On the other hand, building that infrastructure would be useful anyway, in
> some cases, such as constrained-bandwidth nodes.  That way the
> constrained-bandwidth nodes could prioritize which streams are
> ===
> Bill Nickless      +1 630 252
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