[c-nsp] Effect of IGMP version on IGMP Snooping

[John Neiberger]

The hosts are still running IGMPv2, but we will be upgrading them to
v3 later. There is one particular piece of equipment that we will be
replacing in the very near future that can only run v3, so we wanted
to change the switch to v3.  To explain a bit more, this particular
part of the network is really just one VLAN, no router, but IGMP
snooping is enabled on the switch (multiple switches, actually.) So,
my only thought is that switching to v3 in midstream while traffic was
flowing somehow broke IGMP snooping even though we have verified that
IGMP v3 snooping is enabled. We can't explain it, so we're sort of
grasping for straws.

We will be adding some additional monitoring and then conducting a
test to see if we can spot the problem.

On Mon, Jan 24, 2011 at 6:11 PM, Aaron <ariemer at amnet.net.au> wrote:
> Did you enable IGMPv3 on the switch?
>
> How did you ensure all your hosts were running IGMPv3?
>
> From memory I had to registry hack the windows hosts to get it to run the
> expected version.
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of John Neiberger
> Sent: Tuesday, 25 January 2011 7:16 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] Effect of IGMP version on IGMP Snooping
>
> We have a flat layer two network with IGMP snooping turned on. We are
> currently running IGMP v2 everywhere, but we need to enable v3. We
> tested this a few nights ago and found that switching to v3 caused a
> disruption. Everything started working again after we switched back to
> v2. This doesn't make much sense to me.
>
> We have an interface acting as IGMP querier, so snooping seems to be
> working. But why would changing IGMP versions cause any disruption?
> And why would switching back to v2 suddenly make it work?
>
> If it matters, this is a Cisco 4948 running 12.2(25).
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