[AG-TECH] IGMPv3, Source Specific Multicast, fully supported in Windows XP

[Jeffrey Eschbach]

> Close.  You're right on with the SSM mechanism.  But in the ASM case, the
> traffic goes to the RP and then a subset gets converted into MSDP Source
> Active messages and are flooded.

Bill, thanks for clarifying.  My answer to Jay's example question was
coming from a simple, single-domain perspective... your answer does a
much better job of explaining what would actually happen on Abilene,
which handles inter-domain multicast.

Jeff



Bill Nickless wrote:
> 
> At 10:49 AM 8/16/2002 -0500, Jeffrey Eschbach wrote:
> >I don't think IGMPv3 actually is involved on the
> >source side... the router just needs to know that it should not forward
> >traffic in the SSM range unless it has received a join.  (For ASM range,
> >traffic would go to the RP and then receive a "register stop" to keep
> >the traffic from leaving the network.)
> 
> Close.  You're right on with the SSM mechanism.  But in the ASM case, the
> traffic goes to the RP and then a subset gets converted into MSDP Source
> Active messages and are flooded.  When a remote PIM domain notices the
> active source and sends source-specific joins, the traffic leaves the local
> PIM domain and gets sent towards the receiver.
> 
> In my opinion, this is one of the fundamental flaws of the current Internet
> multicast architecture.  The architectural assumption is that the Internet
> is analogous to an old-fashioned 10Base5 Ethernet segment--nothing needs to
> be done before putting a packet on the wire.
> 
> Since RFC 1112 laid down that architecture, the Internet community has
> learned that the best known way to route multicast traffic is via
> source-rooted distribution trees.  So there's a race condition--the
> source-rooted distribution tree can't be created until the network knows
> there's a source.  But if the network only discovers a source when it puts
> a packet on the wire, it's too late to create those source-rooted
> distribution trees.
> 
> SSM gets around this problem by making the receivers identify the source to
> the network before the source goes active.
> 
> MSDP gets around this problem by flooding the knowledge of active
> receivers, and the first packet of the source's traffic, independent of the
> source-rooted distribution trees.
> 
> ===
> Bill Nickless    http://www.mcs.anl.gov/people/nickless      +1 630 252 7390
> PGP:0E 0F 16 80 C5 B1 69 52 E1 44 1A A5 0E 1B 74 F7     nickless at mcs.anl.gov

-- 
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Jeff Eschbach                              eschbach at motorola.com
Networks and Infrastructure Research
Senior Staff Engineer, Motorola Labs Internet2 Initiative
http://internet2.motlabs.com              Fax:    (847) 576-3240
Desk: (847) 538-5846                      Mobile: (847) 980-2240