From: Petr Lapukhov (petrsoft@gmail.com)
Date: Wed May 03 2006 - 13:46:27 ART
Hello Chan,
1) Source may send IGMPv2 leave if it was multicast receiver, for some other
groups, at the same time. In any other case, source simply stops sending
multicast
packets. No specific singnalling is employed for multicast sources.
2) Within PIM Dense mode, constrained flooding model is implemented. That
is,
packets from ALL sources are flooded out of all PIM-enabled interfaces on
every
PIM router. Next, RPF checks take care of potential loops.After the flooding
the
"first wave", unneeded links are pruned - PIM routers that have no receivers
initiate prune messages. This is standard behavior.
As a result, we have tree-like distribution structure, where leafs of the
tree may
act as sources or as receivers. Every (S,G) pair has state installed on
every
interested PIM router (i.e. router that have receivers for particular
group).
Within this model, every source is treated equally. That is, first hop PIM
router simply
takes multicast packet for a (S,G) pair, and forwards its down on every
non-pruned
interface.
Note, that the same interface could forward packets for one (S,G), pair and
discard
packets for another.
HTH
Petr
2006/5/3, Chan Hong <chan_hong33@yahoo.com>:
>
> Dear all,
>
> I have 2 multicast questions want to ask but my concept of multicast is
> very weak because I'm still reading the books. Please point out if I have
> any wrong(s).
>
> Question 1:
> Under IGMP version2, when members leave the group, they will send the
> leave packet to the 224.0.0.2(all multicast router).
> What if the source(sender) leaves the group? Does it do the same
> thing?(under IGMP action)
>
> Question 2:
> Under PIM Dense mode, it is rooted at source, SPT. In the book's
> example, all of them are only 1 source exists in the network.
> What if there are multiple sources? How does the PIM router select the
> source?
>
> Regards,
> Howard
>
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