[c-nsp] nexus 7k IGMP QUERIER on HSRP interface?

Chris Marget chris at marget.com
Fri Apr 19 19:28:16 EDT 2013

On Fri, Apr 19, 2013 at 4:13 PM, Jeffrey G. Fitzwater
<jfitz at princeton.edu> wrote:
> How should an igmp querier be configured if the interface is also
> configured for HSRP?

> "vlan configuration  (vlan#) "
> "ip igmp snooping querier A.B.C.D"
> --------------
> Do I use the VIP IP or the interface IP.

You only need the IGMP snooping querier configuration in 'vlan
configuration' context if you're not running PIM on the interface
because it's a link-local multicast with no multicast routing

If that's the case, it really doesn't matter what IP you use, but
using the HSRP address would make the IGMP querier election (it's a
little surprising that this runs, but it does) kind of wonky, so I
wouldn't do that.

I *think* (some?) Catalysts which support this L2 querier feature send
their queries from, though I haven't tested it for a long

I have experimented a bit with exactly the scenario you're talking
about much more recently.

The IP you configure here will be stamped in the IGMP queries. Nothing
more. The "router" portion of your Nexus doesn't even need to hear the
reply, so you could use an address you don't own. These queries exist
only to make hosts reply for the benefit of IGMP snooping L2 gear.
It's totally synthetic and doesn't really matter.


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