IGMP Query messages - need clarification

Answered Question
Jan 24th, 2011

Hello all,

I  am reading the CCIE R&S 4th edition book and came across something  in the multicast section that isn't exactly clear about IGMP query  messages.

It  reads that General Query messages are sent out to determine if any host  wants traffic from any group - with a default of 125 seconds b/t  messages

Also it reads that Host membership query messages are  sent on each interface to see if any host wants traffic from any group -  with a default of 60 seconds b/t messages.

Finally it reads that  Group specific membership queries are sent to see if any hosts want a  specific group's traffic - which is sent after a leave message for a  particular group is sent.

I  understand the group-specific query messages, but my question is - what  is the difference between General Query and Host Membership Query  messages?  It sounds as if they do the exact same thing, but with  different timers???  The book doesn't dive into this explanation, and I  am having a hard time finding the answer on the web.

Any help is greatly appreciated.


Thanks,
Sanjay

I have this problem too.
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Correct Answer by FIDLAFIDLA about 3 years 2 months ago

If you are hunting for CCIE, it'll be best to find answer yourself, it gives you real knowledge, not only answer to one question that you have now. You must be able to search for answers your own... You can use documentation, RFCs aso.


So I personaly recommand not to read the rest of this, because it try to answer your question

There are 3 versions of IGMP. First mentioned only one type of query "Host membership query". Second version use 2 types of "membership query", general and group-specific. So there is no "host membership query" in IGMPv2. If terms inside of book are not clear in it.... RFCs are.

If you search documentation a little bit... you will find command for change of interval for igmp queries...

ip igmp query-interval (http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_02.html#wp1052526)

Inside usage section you see that 125 seconds ("RFC" interval) is not used by IGMP cisco implementation... it is by default 60 seconds. (and 60 is interval that you see if you type "sh ip igmp int " command.

HTH

Tomas

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Correct Answer
FIDLAFIDLA Wed, 01/26/2011 - 03:14

If you are hunting for CCIE, it'll be best to find answer yourself, it gives you real knowledge, not only answer to one question that you have now. You must be able to search for answers your own... You can use documentation, RFCs aso.


So I personaly recommand not to read the rest of this, because it try to answer your question

There are 3 versions of IGMP. First mentioned only one type of query "Host membership query". Second version use 2 types of "membership query", general and group-specific. So there is no "host membership query" in IGMPv2. If terms inside of book are not clear in it.... RFCs are.

If you search documentation a little bit... you will find command for change of interval for igmp queries...

ip igmp query-interval (http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_02.html#wp1052526)

Inside usage section you see that 125 seconds ("RFC" interval) is not used by IGMP cisco implementation... it is by default 60 seconds. (and 60 is interval that you see if you type "sh ip igmp int " command.

HTH

Tomas

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Posted January 24, 2011 at 5:00 PM
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