IGMP v2 Designated Querier

Unanswered Question
Aug 2nd, 2007

I was reading the 642-901 vol 2 study guide about IGMP v2 and it was discussed there that to determine the Designated Querier the routers:

"When there are two IGMP routers on the same Ethernet segnet (broadcast domain), the router with the highest IP address is the designated querier." - p247

I googled around to check if there are some documents that support this and I found this site:


it says:

"If a multicast router hears a Query message from a router with a

lower IP address, it becomes a Non-Querier on that network."

So if I understand it correctly if the router sees an IGMP router with a lower IP address it steps back (becomes a non-querier) and lets the lower ip address router become the designated querier.

So this is confusing. Can anyone confirm which is true? Is the study guide wrong?

I have this problem too.
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CSCO10892433 Fri, 08/03/2007 - 17:33

Hi, Eric

Excerpt from Routing TCP/IP vol2,page 537:

"The router with the lowest IP addresss becomes the IGMPv2 querrier."

There is also a lab senario on this page. If you have routers of your own, You can set up this senario and test which router becomes the querier by typing "show ip igmp interface" on each router. When there is a conflict among different documents, it's a good idea to let the routers tell you the truth.If you don't have any router to test, let me know,I can do this test for you on my home lab after I go home.



royalblues Sun, 08/05/2007 - 13:55

Yes, they preempt.

The Router with the lowest IP address becomes the querier and the other one goes silent




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