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

[Stig Venaas <[e-mail]>]

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?
>