The MPLS WG Archive

[IJsbrand Wijnands <ice@cisco.com>]

Hi Thomas,

>> It looks to me that the table selection is a local policy and does not
>> necessarily need to be the same on each LSR. You may want to use a
>> MuRIB between 2 LSRs just to make Multicast divert from Unicast for a
>> specific link. How these two tables are used is up to the operator to
>> define. It does not seems to be something the draft must spell out.
>
> I don't think that the above is exact: to ensure no routing loop is
> created, consistency between SPF calculated by different routers is
> needed.
>
> If, for instance, a multi-topology IGP is used, then we may want to say
> that all routers should use the same topology to lookup upstream
> interface to LSP root.

I agree that with a multi-topology IGP it is the most obvious way to 
build your tree. But it is still possible to only run a multi-topology 
in a sub section of the network where you have specific needs to do so. 
I don't think it is up the mLDP draft to limit the scope.

>
> We could say for instance that multicast topology MUST be used if
> multi-topology ISIS is used (or an alternate new multi-topology 
> topology
> ID, if we don't like reusing the one dedicated to IP multicast).
>

I see multi-topology IGP as different unicast tables. These tables 
represent different topologies where you may want to pick one for mLDP 
build trees. If we don't want to call one the multicast IGP, how do you 
want to define this in the draft?

Thx,

Ice.


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