[nsp] more than 2 sites with Q-in-Q

[Lars Erik Gullerud]

On Tue, 2004-05-11 at 15:22, tesinska-predstoleti at yahoo.com wrote:
> Hello!
> 
>   I got question concerning on Q-in-Q. Can I connect more than two
> sites of one customer using Q-in-Q VLAN?
> 
> for example:
> There's core QinQ network with 3 switches connected in triangle with
> trunks. I connect to every core switch customer switches and make
> connections dot1q-tunnel. Will it be working OK? Is there something
> more to be configured?

It works, but you risk some excess flooding of broadcast/multicast and
unknown unicast packets. Consider the following customer VLAN setup:

Site A: VLAN 11,12,13
Site B: VLAN 11,12
Site C: VLAN 11,13

All of this is transported through your core with outer tag 500.

VLAN 11 is shared among the three, while VLAN 12 is only between sites A
and B, and VLAN 13 is only between sites A and C.

Since the switches in your core are only seeing the outer tag 500,
traffic for VLAN 12 will still be flooded to site C and traffic for VLAN
13 to site B. Of course, the customer can (should!) block this on their
side of the trunks, but you will still be flooding all of this through
your core. For three sites with 3 VLAN's this is not much of a problem,
but build a large number of sites on Q-in-Q where the inner VLAN's are
not identically shared, and you will have a lot of useless traffic on
your links...

/leg