Re: [magma] Question about IGMP host implementation

Bharat Joshi <> Wed, 12 October 2011 11:25 UTC

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From: Bharat Joshi <>
To: Indranil Bhattacharya <>, Kunal Shah <>
Date: Wed, 12 Oct 2011 16:53:27 +0530
Thread-Topic: [magma] Question about IGMP host implementation
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How is a switch has two different subnets on its two ports? Typically switch divides the broadcast domain. Right?

From: [] On Behalf Of Indranil Bhattacharya []
Sent: Wednesday, October 12, 2011 2:05 PM
To: Kunal Shah
Subject: Re: [magma] Question about IGMP host implementation

Hi Kunal,

             Yes it should. The scenario that I have in mind is a switch whose mrouter interface is in vlanA and igmp joins are received on an interface in vlanB. In this case, query coming from vlanA(different subnet) has to be answered by hosts in vlanB.


On Wed, Oct 12, 2011 at 6:08 AM, Kunal Shah <<>> wrote:
Hi all,

Can an IGMPv2 host respond to a general query originated from a subnet other then its own?? RFC 2236 states:

""query received" occurs when the host receives either a valid
     General Membership Query message, or a valid Group-Specific
     Membership Query message.  To be valid, the Query message must be
     at least 8 octets long, and have a correct IGMP checksum.  The
     group address in the IGMP header must either be zero (a General
     Query) or a valid multicast group address (a Group-Specific Query)"

There is no requirement for the source address to be on the same subnet as the host.


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