[trill] Smart Endnodes and FGL Interaction

[Radia Perlman <[e-mail]>]

I got an off-line question that might be worth explicitly answering in the
draft, next time we do an update of the smart endnode draft.

The question came about because of someone wondering howthe  smart endnodes
design interacst with the FGL design, and what relationship the outer VLAN
is to the FGL.

I believe that a TRILL encapsulated packet to/from a smart endnode should
look exactly the same as if it were being forwarded to an RBridge, still
encapsulated.

So the answer is that the outer VLAN is the Designated VLAN for the link.
 (as has been the case for TRILL for years, each link is assigned a
Designated VLAN by the DRB, and all TRILL-encapsulated packets are
encapsulated with that VL as the outer VLAN).  The Designated VLAN will
always be a VL, not an FGL.

The inner VLAN will either be VL or FGL, but it will be filled in by the
smart endnode (and delivered to the smart endnode) exactly as the first RB
would have encapsulated it.  If it's supposed to be a 24-bit VLAN, it will
be an FGL.  If it's supposed to be a 12-bit VLAN, it will be a VL.

Hope that adequately answers the question that nobody on the mailing list
asked.  :-)

Radia