Dot1q or ISL?

[cro9uk]

I am creating vlans at a site and Cisco documentation states that Cisco prefers ISL over Dot1q. Can someone explain to me the difference and what's wrong with encapsulating with dot1q?

[milan.kulik]

There is nothing wrong with 802.1Q.

It's a IEEE standard encapsulation using 4-byte header.

ISL is Cisco proprietary, using 30-byte header, considered obsolete nowadays.

Some Cisco devices even don't support ISL (Cat2950, e.g.)

I think your documentation must be pretty old.

See http://www.cisco.com/warp/public/473/185.pdf for ISL and 802.1Q comparing, e.g., or http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Technologies:Trunking&viewall=true for a lot of trunking articles.

Regards,

Milan

[cro9uk]

Thanks Milan, i got the PDF from the cisco site yeterday! i'm glad you mentioned the 2950's because those are what i am using.