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

[Andrew Fort]

On 11/05/2004 11:55 PM, Mikael Abrahamsson wrote:

>>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...
>>    
>>
>
>Noteworthy is that even with q-in-q you still carry all your customers 
>different MAC adresses, so pretty soon you're going to run into that 
>limitation of the 3550.
>  
>

One other thing to be wary of with Q-in-Q is to watch the ingress points 
to the tunnel.  If you have the same MAC address (say a router interface 
that is RFC1483 bridged onto ATM) appearing in multiple entry points, 
the Q-in-Q cloud will see the same MAC address, on the same (outer) 
VLAN, appearing on multiple ports (if the two ingress points are two of 
the ingress points of your Q-in-Q tunnel) -- causing MAC flapping and 
associated connectivity problems.

Obviously this is a design issue and not a hardware problem, but where 
you have multiple ATM interconnects with other carriers (and have to use 
Q-in-Q from your 1483 bridge say, due to lack of VLAN translation 
features), it can bite.

-afort