Re: [magma] Question about IGMP host implementation

Kunal Shah <> Wed, 12 October 2011 15:48 UTC

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From: Kunal Shah <>
To: Bharat Joshi <>, "" <>
Date: Wed, 12 Oct 2011 11:47:59 -0400
Thread-Topic: Question about IGMP host implementation
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Subject: Re: [magma] Question about IGMP host implementation
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Hi Bharat,

The security consideration addresses the processing of a report from a different subnet on the router. My question pertains to the processing of a Query from a different subnet on the host.


-----Original Message-----
From: Bharat Joshi [] 
Sent: Wednesday, October 12, 2011 4:20 AM
To: Kunal Shah;
Subject: RE: Question about IGMP host implementation

Hi Kunal,

        I think to keep the security tight, it is better to not respond to queries received from a source address which does not fall on a subnet on that interface. Please note that this should be done only broadcast interfaces. It may not work on point-to-point links.

        If you look at the security consideration in RFC 2236, it is mentioned that for reports, the above check should be done.

From: [] On Behalf Of Kunal Shah []
Sent: Wednesday, October 12, 2011 6:08 AM
Subject: [magma] Question about IGMP host implementation

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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