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Hi all,

I'm a bit confused about the methods used when two routers are connected to the same network (with some receivers), assuming they have the same metric's to the source as seen from the IGP. Afaik igmpv2 has a method for querier election with the outcome that the router with the lowest ip is the active querier/forwarder of the traffic to that segment.

1.) When looking at PIM (also using IGMPv2) they have a forwarder/DR election based on the router with the highest ip address. Doesnt PIM DR election and IGMPv2 querier election conflict with eachother?

2.) How would PIM do a querier/forwarder election if it's using IGMPv1?

3.) If DVMRP is used on one router and PIM on the other; PIM would elect one querier with the highest IP, and DVMRP would elect the one with the lowest ip because it uses IGMP?

I hope someone can clear this up for me. :)

Thanks,

Wouter

We need to look at them as two seperate functions.

* DR is responsible for "PIM" Register/Prune messages toward RP.

* IGMP Querier is responsible for IGMP "host-query" messages.

With IGMPv1, since there is no concept of Querier, PIM DR typically serves both the PIM routers and IGMP hosts (think of it as an additional responsibility).

With IGMPv2, there IS an election, so router with lower ip address serves the hosts (as an IGMP Querier) and router with higher ip address serves PIM routers (as PIM-DR).

HTH

thanks msaqi,

I somehow thought that the interfaces pointing to the source needed to be pim enabled -only-. But also the interfaces pointing to the receivers need to be added apparently. :) As soon as i enable pim on those interfaces it automagically enabled igmp also. :)

You are right. Enabling PIM also enables IGMP automatically. That is because only multicast enabled interfaces can get the stream. If it is not enabled on an interface, it will not show up in oil list. We may have to consider alternate solutions in that case (i.e. converting multicast to broadcast etc.)