Re: [Isis-wg] MPLS IGP label in ISIS

["Ilya Varlashkin" <[e-mail]>]

Peter,

> -----Original Message-----
> Source Routing with MPLS label stacks. Yes its possible to do that and to
> setup any kind of traffic engineered path you want not just shortest
without
> having to install per flow state at every hop.
> 

No, it isn't source routing - we would still do 'destination-based' routing,
just we would know labels for whole IGP domain rather than for directly
connected neighbours.

> This kind of approach would work well with an SDN controller since it
would
> eliminate having to send state installation messages to every hop along
the
> path.
> 

You could use central controller to do offload certain PATH calculations,
but you wouldn't be able to setup do arbitrary PATH (like with RSVP-TE).
However using central controller is not required - the decision is already
done by SPF, only difference is we have no label information for each and
every destination, so we can craft label stack in such way as to cause
desired label operation at certain hops with _existing_ label (this is not
the same as achieving "desired traffic flow" which would need more labels).

> As you say however most hardware is limited to how many labels they can
> push, 3 or so, which limits your diameter unreasonably.
> 

Label stack based on global labels is not different from label stack based
on RSVP-TE labels, so this isn't an issue.

> Source Routing in general however has a bad name because of issues
> associated with IPV4 and V6 source route header options that can be used
> for all kinds of nasty DOS and Man-in-the-Middle attacks, unfortunately

Since what's proposed is not source routing, the header options are not
used, and therefore the global labels have no more no less to do with DoS
and MiM than locally-unique labels.

/iLya