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

[Brian Haberman <[e-mail]>]

Hi Stig,
      Thanks for the clarification...

I am curious if the following two additions would address this issue 
without delaying the advancement of the documents to Internet Standard.

1. In Section 7.2.1 - Add this to the last paragraph : "It is 
recommended that implementers provide a configuration option to disable 
use of Host Compatibility Mode to allow networks to operate only in SSM 
mode. This configuration option should be disabled by default."

2. In Section 7.3.1 - Add an additional bullet : "It is recommended that 
implementers provide a configuration option to disable use of 
compatibility mode to allow networks to operate only in SSM mode. This 
configuration option should be disabled by default."

Regards,
Brian

On 4/8/24 5:26 PM, Stig Venaas wrote:
> Hi Brian
> 
> I don't think changing defaults would be sufficient. My concern (and I
> think that is what others are concerned about as well) is that hosts
> and routers fall back to older versions when there is an older version
> querier, as specified in 7.2.1 and 7.3.1. Regardless of the default,
> it says that they must change mode or fall back.
> 
> I think we need some text where we RECOMMEND that hosts and routers
> have a knob that disables compatibility mode and makes the host/router
> always operate in IGMPv3 mode. This should of course be off by default
> (fall back as usual). I'm happy if there is a more lightweight
> approach that I'm not seeing.
> 
> Regards,
> Stig
> 
> On Tue, Apr 2, 2024 at 12:10 PM Brian Haberman <[e-mail]> wrote:
>>
>> Hi Hitoshi,
>>
>> On 3/20/24 10:01 PM, Hitoshi Asaeda wrote:
>>>
>>> I thought what we need to clarify in DS IGMPv3/MLDv2 RFCs is that, as Brian mentioned, we can simply add recommended default settings for the compatibility mode variables. That’s all, I thought.
>>>
>>> But you remind me of the following four situations.
>>>
>>> 1. querier = SSM capable, forwarder = SSM capable -> no fallback
>>> 2. querier = SSM capable, forwarder = non-SSM capable -> fallback
>>> 3. querier = non-SSM capable, forwarder = SSM capable -> no fallback (and SSM capable router must become (replace) querier?)
>>> 4. querier = non-SSM capable, forwarder = non-SSM capable -> fallback
>>>
>>> I wonder how above 2 and 3 are clearly considered in some RFCs?
>>
>> Which RFCs are you worried about? I think 3376 and 3376bis cover this in
>> section 7.3 with discussion of the compatibility mode and group
>> compatibility mode variables. We would augment that discussion with a
>> recommendation that those compatibility mode variables default to IGMPv3
>> mode.
>>
>> Table 9 in section 7.2.1 already indicates that hosts default to IGMPv3
>> mode. We need to indicate a similar default in section 7.3.1.
>>
>> Regards,
>> Brian
>>
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