[rbridge] Pseudo-node nickname

[Erik Nordmark]

A few questions that I didn't bring up in the meeting since we were 
short on time.

You said that the pseudo-node nickname is not used for multicast.
Is that a statement about the destination nickname (which identifies the 
tree)? Or is it also a statement about the source nickname?
I would assume the source nickname would be a pseudo-node even for 
multidestination frames, since the egress rbridges would learn from the 
source nickname.

Currently TRILL can handle a link being partitioned as long as there is 
at least one RBridge in each partition; a DRB will be elected for each 
partition.
With pseudo-node nicknames this adds some complexity. I think each DRB 
will need to pick a unique pseudo-node nickname after they detect a 
partition of the link (but how do they reliably detect the difference 
between a RB failure and a partitioned link?). If they don't packets 
will be routed to an egress RBridge which thinks it is attached to the 
same link as the endnode, even though it isn't due to the endnode being 
in the other half of the partitioned link. Hence packets will be dropped 
on the floor.

Perhaps you can clarify those parts.

Thanks,
     Erik