Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

VLANs: basic question...

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.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: VLANs: basic question...

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

1 REPLY

Re: VLANs: basic question...

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

76
Views
0
Helpful
1
Replies