[pim] Re: Multicast routes to end user devices?

[Brian Haberman <[e-mail]>]

Below...

On 5/13/24 1:42 PM, Stig Venaas wrote:
> Hi Linus
> 
> Interesting questions.
> 
> I am pretty sure there is no protocol defined, ICMPv6 RA or otherwise,
> that can tell the host which interface to use for multicast.
> 
> Currently I believe most host stacks need explicit configuration, if
> this can be controlled at all. I haven't tested this in a long time,
> but I believe you can control this on Linux by modifying the routes
> you mentioned.
> 
> I have a couple of ideas on what host stacks potentially could do. One
> is to select an interface where there is an igmp querier. Also, I
> would say, prefer an interface with IGMPv3 querier if possible. Also,
> base on unicast routing, any SSM reports, IGMPv3 include mode with
> sources, could send the report on the interface that has the best
> route for the source.
> 
> Do you think it would be worthwhile allowing RAs to indicate that an
> interface should be used for multicast, or having some preference.
> What do others think?
> 

This would only work on multi-interface machines if all the upstream 
routers were managed by the same provider. I have a dual-homed network 
and I get two default routes, one from each upstream.

I know there has been periodic discussions on how to provide more data 
to hosts in order to help them make the correct decisions related to 
multicast traffic, but they always tend to die out due to lack of 
interest in sharing topological information to customers.

I would favor the local approach of heuristics with what a host can 
detect (e.g., presence of IGMP/MLD queriers).

Brian