[c-nsp] IEEE 802.1ad vs Cisco's Q-in-Q

Tassos Chatzithomaoglou achatz at forthnet.gr
Tue Nov 14 14:04:38 EST 2006

Does anybody know when (and if) is Cisco going to support the offical 802.1ad?

If i understand correctly, Cisco's Q-in-Q implementation doesn't support different ethertypes for 
inner & outer tags, which probably means that Cisco switches don't care whether a frame is single or 
double-tagged, as long as the outer ethertype is 0x8100 (or equal to the one configured).

So, are there any performance limitations when a double-tagged frame passes through a 6500 (or other 
switch)? What happens if the inside of every frame has to be checked (because of QoS) and a 
double-tagged frame is found? Does the switch send the double-tagged frame to the cpu because it 
cannot recognise the protocol inside it?


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