Subject: IGMP- DR and querier

From: Ali Boudani <[email-masked]>
Date: Wed, 06 Jun 2001 14:53:44 +0200

If the DR and the querier are different in a network, how the DR knows
about the group memberships??
(this case can exist in PIM where DR is the highest IP address and the
querier is the lowest IP address)
Thanx

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From: David Barnett <[email-masked]>
Date: Wed, 6 Jun 2001 11:36:31 -0400

> querier is the lowest IP address)

In my understanding...

The goal of the querier mechanism in IGMP is not to have one machine on a lan 
keeping all of the group state, but instead to reduce the amount of routing 
trafic. 

In the case of IGMP the membership reports are sent to a multicast group,
which allows any router on the lan to listen to reports without actively 
querying. Any router on the lan can and will need to listen to these reports to keep track of group memberships. In the case of IGMPv3 all membership reports 
are multicast to the IGMPv3-CAPABLE multicast routers group. For IGMPv2 or v1 
the reports are multicast to the group of interest. 

So basically, the fact that a router is not querier only relieves it of the
duty of querying the multicast listeners. It still must listen and process
the IGMP traffic.

-Dave

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From: Christopher Thomas Brown <[email-masked]>
Date: Wed, 06 Jun 2001 11:33:57 -0400

A non-querier keeps take of group memberships also. It just never sends
out query messages.

ctbrown

On Wed, 06 Jun 2001 14:53:44 +0200