Re: [Isis-wg] [rbridge] Why is MTU discovery important?

[Robert Raszuk <robert at raszuk.net>]

Hi Radia,

> Keeping the Hello mechanism exactly as it is in IS-IS today will not 
> work for TRILL.
> That should be the end of discussion. Not padding the Hellos obviously
> works for robustly finding neighbors, and is a trivial change. The
> only thing that gets lost is MTU discovery.
>
> The only feasible choices at this point are:
> a) only do unpadded Hellos, and live with weirdnesses due to not
> testing MTU size, deferring MTU discovery to the future
> b) do unpadded Hellos, and come up with a mechanism for MTU discovery now.
> It would be easy to do so.

+

> So to really test the MTU requires a padded packet,
> (but it need not be (and MUST NOT be, for TRILL) the same, simultaneous mechanism
> as finding neighbors, such as layer 3 IS-IS which does not see neighbors that can't
> be reached using the largest packets.)

So how about option c) which would leave current L3 ISIS Hellos as is 
today and define a new TRILL ISIS Hello mechanism ? Seems to me like 
quite simple and trivial solution to accomplish without any compromises.

Of course if we down the road find that minor changes like this will be 
required to other functions of today's ISIS it will be also easier to 
separate L3 ISIS from ISIS twicked for TRILL and perhaps even run it 
fully independently.

Cheers,
R.