[RTG-DIR]Re: [pim] Re: [Last-Call] Re: Rtgdir last call review of draft-ietf-pim-3810bis-10

[Brian Haberman <[e-mail]>]

Hi all,
      Deprecating a feature does not require that feature to be removed 
from existing standards, so I think we all agree there is nothing to be 
done with the MLDv2-bis specification.

      To Toerless' question about Rtr-Alert was left in MLDv2, I recall 
having conversations around that time about Rtr-Alertss. Concerns were 
raised about code complexity for backwards compatibility, so the 
consensus was to leave Rtr-Alerts in the new version of MLD. I do know 
of some code bases that don't check for their existence and operate just 
fine if the Rtr-Alert isn't in the packet.

      Éric made reference to an MLDv3, which I am unaware of, but would 
be the right place to remove Rtr-Alerts if the backwards compatibility 
concerns are mitigated.

Regards,
Brian

On 7/24/24 4:27 PM, David 'equinox' Lamparter wrote:
> On Tue, Jul 23, 2024 at 10:35:25PM -0700, Stig Venaas wrote:
>> The MLDv2 bis document is not defining a new protocol, we are just
>> progressing MLDv2 to Internet Standard. We should and cannot make any
>> changes that would render existing implementations non-compliant,
> 
> Even though I threw in the mail about this, I don't have a strong
> preference to making any change here.  The room discussion in 6man on
> the RA draft brought up the MLDv2 bis doc and it wasn't clear what's
> going on -- and if there is something to be done, it'd be rather poor
> timing.
> 
>> and also, we want to only have protocol definitions that have multiple
>> implementations and known to work well. Removing RA would be a pretty
>> big change.
> 
> I don't think removing RA is on the table.  If anything, I think it
> would be weakening the requirements to check that RA is present, i.e.
> allowing receive processing without RA.  It would need to remain a MUST
> to include it on send though, as the sender has no idea if the receiver
> (be it router or snooping switch) allows this.
> 
>> I'm not sure why MLDv2 is defined with RA, might it make a difference
>> to snooping switches?
> 
> I don't believe it does, AFAIK the same mechanisms filter out e.g.
> ICMPv6 RA guard, which doesn't have router alert on it.
> 
> Cheers,
> 
> 
> equi
> (David)
> 
> 
> P.S.: our (relatively recent, 2yo) MLD implementation requires RA;  if
> anything I'd like to know if I can and/or should remove that check.
> https://github.com/FRRouting/frr/blame/bd86964db816ba1ac628f1b1f5099fd35f157ea5/pimd/pim6_mld.c#L1712