[c-nsp] dot1q tunnelling presentations

[Sam Stickland]

Hi,

I have a question about cisco's dot1q tunnelling implementation, that the 
documentation doesn't seem make immediately clear.

Is it possible to reverse the direction of the tunnelling?

For example?

Switch C-A ---- Switch P-A ++++++ Switch P-B ---- Switch C-B

The (P)rovider is giving the (C)ustomer a P2P link with a single VLAN for 
their use. The link between C-A and P-A, and P-B C-B is a dot1q trunk, 
that carries a single vlan, call it vlan X.

Can Switch C-A and C-B tunnel VLANs over the providers single VLAN. ie. 
The tunnelling takes place on the client's switches and not the providers.

It seems to me that it's simply a case of where the 4byte VLAN id shim is 
added? I'd like it to be added on the Customer switches in the above 
diagram, rather than the providers.

Something like:

switchport mode dot1q-tunnel
switchport mode access vlan x

on C-A and C-B would achieve this, if the ingress and egress notion of the 
switchports could be reversed? (So it's spits out tunnelled VLANs, rather 
tunnels what it sallows).

Perhaps it's possible to do this by burning an extra port at each end, 
though I could see spanning tree loops happening this way.

Sam