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

[Stig Venaas <[e-mail]>]

Hi

I've updated the 3rd slide now, I think I did as you suggested Brian.
There are now 2 different actions, one is recommending new behavior,
the other is mandating new behavior. And as I wrote, I don't think we
can put anything that would make implementations that are currently
compliant with 3376 become non-compliant. If we make a recommendation,
it may be OK as they would still be compliant if not following the
recommendation, but I don't think we can mandate new behavior.

Stig

On Wed, Mar 20, 2024 at 4:21 PM Stig Venaas <[e-mail]> wrote:
>
> Hi
>
> To add to this. If a router only supporting IGMPv2 is brought up on
> the LAN, it will break SSM regardless of the querier election if this
> router happens to become the DR. There is no way we can avoid this.
> Also, in general, pretty much anything can go wrong if a rogue router
> or a router with wrong config is present. I think the most common way
> for pim to break is that some device is accidentally becoming the DR
> and not having the correct config.
>
> One more thing. I don't think we can make any changes that would make
> implementations to 3376 become non-compliant. Hence if anything, we
> can not require implementations to change, at most we can recommend
> something.
>
> Regards,
> Stig
>
> On Wed, Mar 20, 2024 at 2:36 PM Leonard Giuliano <[e-mail]> wrote:
> >
> >
> > On Wed, 20 Mar 2024, Brian Haberman wrote:
> >
> > <snipped>
> > |      Personally, it seems like most of the scenarios posited have been related
> > | to old kit or mis-configuration. We can't standardize away those types of
> > | actions. At best, I think we can add recommended default settings for the
> > | compatibility mode variables referenced in section 7.
> >
> > I think this is good perspective here.  Having old hosts that don't
> > support IGMPv3 is definitely a scenario to consider, as you never know
> > what end users are going to stick on a LAN.  And as we discussed in this
> > thread, the spec does a pretty good job of not breaking SSM when old hosts
> > appear on a LAN.  But having ~routers~ on a LAN that don't support IGMPv3
> > seems quite another thing.  Is this really a common scenario worth
> > considering now?  And wouldn't it just be easier to just turn IGMP off for
> > such old routers if you are worried about them spoiling the SSM fun for
> > everyone else?
> >