Hi All,

     I was re-reading RFC 3376 for handling compatibility for lower version of querier.

     In section 7.3.1, it is mentioned that a querier configured to run in V3 mode
     should lower its version when it sees a lower version query on the same
     network. From that time onwards, a router should send the lower version
     queries.

     Now the question is, when this router should revert back to its configured higher
     version? The text in section 7.3.1 or elsewhere does not talk about this.

     Should a timer 'lower_version_querier' be started and updated as and when lower
     version queries are removed? Please note this is not same as other-querier-present
     timer.

     Can someone, who has implemented IGMPv3, let me know how this particular case
     has been handled in their implementation?

Regards,
Bharat
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Indranil,

    Ok. But RFC 3376 clearly says that a router should lower its version to the lowest version of query heard on a network.

    One thing I did not get in your reply is 'Let the v2 updates's it querier timer from v3 query...'. While second part of this statement is clear, I am not sure about the first part. A version 2 querier may/may not support V3 so things won't work any way and there will be multiple number of queries on network which may not be desirable.

    Another thing I did not understand is the last sentence. What do you mean by 'reselection can happen after every general query'? I think RFC 3376 suggested this to avoid multiple queries on a network. If a router do what is suggested in RFC 3376, at least there will be only one query in the network.

    I checked couple of open-source implementation and it seems none of them store this information and always use the highest configured version to send out an IGMP query. Not sure if there was any specific reason for not doing this.

Regards,
Bharat
________________________________________
From: Indranil Bhattacharya [myselfindranil <at> gmail.com]
Sent: Monday, July 19, 2010 1:43 PM
To: Bharat Joshi
Cc: magma <at> ietf.org
Subject: Re: [magma] Query on querier version in IGMPv3

Hi Bharat,

             Do not lower the querier version. Let the v2 updates's it querier timer from v3 query or let it use it's configured query interval. Otherwise, the reselection can happen after every General query.

Thanks,
Indranil

On Mon, Jul 19, 2010 at 10:39 AM, Bharat Joshi <bharat_joshi <at> infosys.com<mailto:bharat_joshi <at> infosys.com>> wrote:
Hi All,

    I was re-reading RFC 3376 for handling compatibility for lower version of querier.

    In section 7.3.1, it is mentioned that a querier configured to run in V3 mode
    should lower its version when it sees a lower version query on the same
    network. From that time onwards, a router should send the lower version
    queries.

    Now the question is, when this router should revert back to its configured higher
    version? The text in section 7.3.1 or elsewhere does not talk about this.

    Should a timer 'lower_version_querier' be started and updated as and when lower
    version queries are removed? Please note this is not same as other-querier-present
    timer.

    Can someone, who has implemented IGMPv3, let me know how this particular case
    has been handled in their implementation?

Regards,
Bharat
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every reasonable precaution to minimize this risk, but is not liable for any damage
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