Re: [magma] A size limit of a Multicast Address Specific Query in MLDv2

Indranil Bhattacharya <myselfindranil@gmail.com> Tue, 28 September 2010 10:47 UTC

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Date: Tue, 28 Sep 2010 16:17:41 +0530
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From: Indranil Bhattacharya <myselfindranil@gmail.com>
To: "K.Kawaguchi" <kawaguti@ysknet.co.jp>
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Cc: magma@ietf.org
Subject: Re: [magma] A size limit of a Multicast Address Specific Query in MLDv2
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Hi Kiyoaki Kawaguchi,

                                Yes, I think it should be split up like
IS_IN report and all the split up packets should follow 7.6.3.2 of rfc 3810.
I have never handled this in code though

Thanks,
Indranil

On Tue, Sep 28, 2010 at 1:08 PM, K.Kawaguchi <kawaguti@ysknet.co.jp> wrote:

> Hi all,
>
> # Only the subject was changed.
>
> I have another question.
>
> About a size limit of a Multicast Address Specific Query in MLDv2.
>
> How is a query transmitted when the number of multicast source
> addresses of a query message is limited by the MTU?
>
> Is a Query split like a Report type IS_IN?
> (It isn't a Query like Report type IS_EX, is it?)
>
>
> RFC3810
> ------------------------------------------------------------------------
> 5.  Message Formats
>
> 5.1.  Multicast Listener Query Message
>
> 5.1.10.  Number of Sources (N)
>
>   The Number of Sources (N) field specifies how many source addresses
>   are present in the Query.  This number is zero in a General Query or
>   a Multicast Address Specific Query, and non-zero in a Multicast
>   Address and Source Specific Query.  This number is limited by the MTU
>   of the link over which the Query is transmitted.  For example, on an
>   Ethernet link with an MTU of 1500 octets, the IPv6 header (40 octets)
>   together with the Hop-By-Hop Extension Header (8 octets) that
>   includes the Router Alert option consume 48 octets; the MLD fields up
>   to the Number of Sources (N) field consume 28 octets; thus, there are
>   1424 octets left for source addresses, which limits the number of
>   source addresses to 89 (1424/16).
>
>
> 5.2.  Version 2 Multicast Listener Report Message
>
> 5.2.15.  Multicast Listener Report Size
>
>   If the set of Multicast Address Records required in a Report does not
>   fit within the size limit of a single Report message (as determined
>   by the MTU of the link on which it will be sent), the Multicast
>   Address Records are sent in as many Report messages as needed to
>   report the entire set.
>
>   If a single Multicast Address Record contains so many source
>   addresses that it does not fit within the size limit of a single
>   Report message, then:
>
>   o  if its Type is not IS_EX or TO_EX, it is split into multiple
>      Multicast Address Records; each such record contains a different
>      subset of the source addresses, and is sent in a separate Report.
>
>   o  if its Type is IS_EX or TO_EX, a single Multicast Address Record
>      is sent, with as many source addresses as can fit; the remaining
>      source addresses are not reported.  Although the choice of which
>      sources to report is arbitrary, it is preferable to report the
>      same set of sources in each subsequent report, rather than
>      reporting different sources each time.
>
> Best Regards
> --
> Kiyoaki Kawaguchi
>
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