Re: switch in the mcast tree

Also, the routers will have to send join messages for traffic to be sent
from the RP (sparse) in the first place so snooping PIM hellos only
applies to dense mode traffic. In the second example the multicast
traffic is encapsulated in unicast (register messages) and sent to the RP
so the switch would not cause an issue their either.

From:
Bryan Bartik <bbartik_at_ipexpert.com>
To:
Bit Gossip <bit.gossip_at_chello.nl>
Cc:
ccielab <ccielab_at_groupstudy.com>
Date:
12/28/2009 05:06 PM
Subject:
Re: switch in the mcast tree
Sent by:
<nobody_at_groupstudy.com>

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.
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

--
Bryan Bartik
CCIE #23707 (R&S, SP), CCNP
Sr. Support Engineer - IPexpert, Inc.
URL: http://www.IPexpert.com
Blogs and organic groups at http://www.ccie.net