Re: switch in the mcast tree

Snooping is done on IGMP and PIM by default. The following excerpt is from:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12
.2_35_se/configuration/guide/swigmp.html#wp1025709

"Multicast-capable router ports are added to the forwarding table for every
Layer 2 multicast entry. The switch learns of such ports through one of
these methods:

Snooping on IGMP queries, Protocol Independent Multicast (PIM) packets, and
Distance Vector Multicast Routing Protocol (DVMRP) packets "

-hth

On Mon, Dec 28, 2009 at 3:36 PM, Bit Gossip <bit.gossip_at_chello.nl> wrote:

> Experts,
> if there is a switch, let's say Cat3750 between the last hop router and
> the mcast receiver, the switch snoops igmp by default and based on that
> knows on which ports to forward mcast frames; that is clear.
> But let's say that the switch is between two mcast routers of the mcast
> tree, or between the source and the first-hop router, then there is no
> IGMP to snoop. How does it behave then?
> - floods mcast frame towards all ports as if it was bcast
> - doesn't forward mcast at all
> - something else
>
> Thanks a lot,
> Bit.
>
>
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Bryan Bartik
CCIE #23707 (R&S, SP), CCNP
Sr. Support Engineer - IPexpert, Inc.
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