Re: [MBONED] [pim] IGMPv3 backward compatibility issue killing SSM

Hi Brian,

I apologize if I repeat and loop back to the same discussion.

Toerless previously mentioned;

> RFC3376 (and currently rfc3376bis too) writes (line numbers from idnits):
> 
> 1837       *  If any older versions of IGMP are present on routers, the querier
> 1838          MUST use the lowest version of IGMP present on the network.  This
> 1839          must be administratively assured; routers that desire to be
> 1840          compatible with IGMPv1 and IGMPv2 MUST have a configuration option
> 1841          to act in IGMPv1 or IGMPv2 compatibility modes.
> 
> The second sentence is either english that i do not understand, or it is in contradiction to
> the first sentence. If there is a configuration option to enable/disable router compatibility
> with IGMPv1/IGMPv2, and i disable this configuration option on my router, then i would
> be in contradiction to the first sentence, wouldn't i ?

I also have the similar feeling, but IMO (as I said previously, too), keeping this backward compatibility mode is Ok. The reasonable solution is that disabling the backward compatibility mode is the default (MUST?). And enabling the backward compatibility mode can be selected by operation (SHOULD? MAY?).
Above rule is applied to any address range, but using SSM address range does not affect anything (i.e., always use IGMPv3/MLDv2 in SSM range). 

What do you think?

Regards,

Hitoshi

> On Feb 22, 2024, at 8:43, Brian Haberman <brian@innovationslab.net> wrote:
> 
> Hi Stig,
> 
> On 1/5/24 11:27 AM, Stig Venaas wrote:
>> Hi Brian
>> I'm personally fine with no changes, if we make changes then I think
>> they should be at most recommendations. Hopefully we will see more
>> widespread IGMPv3 support and this will be less of an issue. It will
>> also help if implementations have IGMPv3 enabled by default.
>> Section 7.2 is the more problematic part, but the issue is mainly with
>> some unmanaged/unexpected device using version 1 or 2 I believe. If
>> there are unexpected pim routers present or some pim router has wrong
>> configuration, then things may break in many ways even if we were to
>> address the v3 fallback. E.g. the unexpected device may become DR and
>> not supporting v3 at all, or not having correct RP configuration.
> 
> I have not seen any suggested text changes for 7.2 to address the unexpected use of v1 or v2. Still open to adding recommendations for default settings of the compatibility mode variables, but haven't heard anyone agreeing with such a change.
> 
> Regards,
> Brian
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