[rbridge] Questions - VLANs & MPLS

[Kris Price]

James Carlson wrote:
> Dinesh G Dutt writes:
>> MPLS format was originally considered and rejected for a few reasons. For 
>> example, we wanted the source and destination RBridge addresses instead of 
>> only the destination RBridge because of the need to support things like 
>> IEEE's congestion management, support troubleshooting tools such as 
>> traceroute and ping within an TRILL cloud etc.
> 
> I think a more important reason for it is that you can't do MAC
> address learning of decapsulated packets unless you know where (what
> encapsulator) they came from.

I wondered about that, but I didn't understand why an RBridge needed to 
do MAC address learning. It seemed that was handled by IS-IS. If I read 
the original paper right that was the intention. (?)

But reading the draft (properly this time) I see MAC learning is now the 
favoured method, with distribution by IS-IS optional. Part of me favours 
this now that I understand it. It means intermediate RBridges don't have 
to maintain information in their FIBs that they're not using.

I guess it was a contentious issue whether learning should've all been 
via a routing protocol, or via learning. Had the former been favoured, 
MPLS label switched paths would've been a feasible forwarding method.

Makes sense now, thanks for your answers :)

Cheers
Kris