[rbridge] Questions - VLANs & MPLS
trill at punk.co.nz
Sat Oct 4 06:25:50 PDT 2008
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 :)
More information about the rbridge