Re: [magma] Multicast Router Discovery - Is it a valid solution?

[Pekka Savola <[e-mail]>]

On Thu, 4 Sep 2003, Brian Haberman wrote:
>      The initial point that should probably be discussed is
> whether people feel that the general approach defined in MRD is
> useful for the task of finding multicast routers.
> 
>      When MRD was first defined, no other work had started on
> IGMP/MLD snooping.  The goal was to define a mechanism that
> would provide switches the capability of quickly discovering
> the location of multicast routers without having to update code
> everytime a new routing or group management protocol came along.
> 
>      At this point, there is also the issue that the snooping
> draft recommends using MRD as a part of an overall switch/snooping
> implementation.

You said "The initial point"; are followup questions to be expected on 
other points?

My brief take is that MRD seems to suffer from a case of lack of clear 
applicability.  This can be seen e.g. by looking at an extension proposed 
for it, draft-ietf-magma-mrdssm-03.txt.  That extends the use of MRD from 
snooping switches to practically every host.

I think we have to be very, very careful here.  Approach like MRDSSM 
doesn't look good.

On the other hand, it may be useful to be able to automate the mechanism
the snooping switches (or IGMP proxies, maybe) could use to to find the
multicast routers.  I haven't looked closely enough in that problem space
to see whether this kind of mechanism is really needed though.

However, my concern is that if we're only interested in router<->snooping 
switch interaction, is this the right solution?  In particular, is the 
solution unnecessarily complex for the task to be done?

Perhaps we could just get around the problem by having the router send a
magic multicast heartbeat packets (e.g. a probe to a designated
224.0.0.x/24 address), using which the switches could figure out what is
the path towards the router(s), as simple as that.

The hosts in the subnet could mess this up, of course, by also sending 
such packets, but that's already the case with MRD, and similar 
countermeasures would apply.

So, to conclude, I'm very concerned with the direction MRD has taken, in
particular whether it's the right way to solve this particular problem.  
But if we end up going for it anyway, I'd sugggest publishing it as
Experimental, not PS.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings


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