From: Tarun Pahuja (pahujat@gmail.com)
Date: Fri Nov 09 2007 - 15:16:55 ART
Nicky,
I would highly recommend you read the following link. It tells
you exactly how IGMP Snooping works.If IGMP snooping is not enabled on the
switch, it would not have the intelligence to read inside an IGMP packet and
would simply flood it across the broadcast domain.
http://www.cisco.com/warp/public/473/22.html#snooping_ov
As Bob suggested you can disable IGMP snooping and statically map multicast
dynamic Content-Addressable Memory (CAM) entries to avoid flooding,
Drawbacks being that it would not be a dynamic process and the traffic would
be send to the client even when it does not want to listen to it as the CAM
entries would not be removed dynamically.
HTH,
Tarun
On Nov 9, 2007 12:58 PM, Bob Sinclair <bob@bobsinclair.net> wrote:
> nicky noname wrote:
> > Hello,
> >
> > If you disable IGMP snooping on a switch, the switch will still
> > forward IGMP messages to and from the host/ router right?
> >
>
> Yup!
> > The difference being that the IGMP messages will be flooded on the
> > vlan. So when the multicast traffic is forwarded to the LAN switch
> > from the router, after the router recieves an IGMP join, now will the
> > switch drop the traffic because it has no entries in the forwarding
> > table, or will it broadcast the traffic out all ports. ( under IGMP
> > conditions, only the IGMP traffic goes via the CPU and the pim traffic
> > goes to the ports listed in the forwarding table).
> >
>
> If you have disabled igmp snooping, then the switch will flood multicast
> in the vlan.
>
> However, there is a scenario where you disable IGMP snooping for a vlan
> and then statically associate a multicast mac-address on a particular
> port or ports. In this circumstance the switch will forward the
> multicast to those ports and not flood.
>
> Hth,
>
> --
>
>
> Bob Sinclair CCIE 10427 CCSI 30427
> www.netmasterclass.net
>
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