ISL tunneling comparible to 802.1q in q?

[emphillips00]

Hi all,

I have searched high and low, and have not found a definitive answer yet so I am hoping someone here can help. 802.1q in q tunneling can be used by a service provider to permit multiple clients to use VTP and send 802.1q tunnels between locations without using up tunnel numbers in the provider's core, and preventing clients from joining other client's VLANs.

However, I am fairly certain that there is no such comparable feature for ISL, but I am not completely positive.

So my question is does an ISP currently using ISL have any choice but to move to 802.1q to offer a client the ability to pass their VLANs across the ISP's network?

Thanks,

Eric

[pkhatri · Accepted solution]

Hi Eric,

I don't believe any such feature exists or is likely to appear in the future. The 26-bytes of overhead contributed by the ISL encapsulation is bad enough but I can't imagine adding another 26 bytes to that...

I would recommend that you use 802.1q tunneling since that is certainly more inter-operable between vendors as well...

Paresh

[flashboy77]

VTP is a Cisco proprietary protocol. Allows switches to propergate VLAN database. ISL and Dot1q are trunking/tagging protocols.

ISL and dot1q are completely different. Dont get confused

[emphillips00]

I understand flashboy, but if you have two sites that are seperated by an ISP, and you are running 802.1q trunking on each side of your link, the ISP can use q in q to tunnel your VLANs across. Additionally, they would have the ability to tunnel layer-2 traffic such as CDP and VTP as well. I was not getting them confused.

My question, which I believe was answered sufficiently, is if the provider is using ISL instead of 802.1q, they would not be able to provide a trunk tunneling service.

Thank you!

-Eric