igmp join-group and receive multicast tarffic

[zillah2004]

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_r/1rprt1/1rmulti.htm

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To have the router join a multicast group, use the ip igmp join-group interface configuration command

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I feel that the above quote is inconsistent with the what I have read recently in the quote below :

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igmp join-group is not needed to enable hosts on a segment to receive multicast traffic. If a host on a segment wants to receive traffic for a particular multicast group the host will respond to the router?s IGMP query messages or send an unsolicited IGMP report message.

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Any clarification ?

Regards

[vladrac-ccna]

Hello Zillah,

You are having problems with multicast lately, right?

ok, I dont see any problems with the first quote.

You really dont need to make the router joing the multicast group in order to make your multicast network work.

I usually use that command for testing purpose, as usually my LAB is only based on devices not hosts I need a way to test it. Then I use the command ip igmp join-group x.x.x.x command to make the router respond to my pings to the multicast IP.

HTH,

vlad

[ariela]

Hi,

The join-group command forces the router to respond "as a host" on its own interface.

It's not closely "necessary" for your multicast network, normally it's used only for testing purpose (to "simulate" an host that joins a specific multicast group when you haven't that but you need to check your multicast topology).

HTH

Andrea