VLANs: basic question...

[carlosignaciotapia]

Hi, there. Sorry for the basic question I'm about to ask but I really need a clear answer.

I've been taught at my Academy that to implement VLANs, basically you can do it with 2 frame labeling methods: ISL and DOT1Q (IEEE802.q). We've also seen that ISL isn't supported for the newer switches and routers, so I got to the conclusion that DOT1Q must be someway better than ISL.

Am I correct? Is DOT1Q better than ISL when implementing VLANs? How's that?

Thanks.

[milan.kulik · Accepted solution]

Yes, you are correct, there are two reasons why to use 802.1q and not ISL:

1) ISL is Cisco proprietary, 802.1q is an open standard.

So ISL is provided only on Cisco devices (even not all of them), 802.1q is supported by most vendors.

2) Overhead: ISL is adding 30 bytes to every frame while 802.1q only 4 bytes.

Regards,

Milan