ISL is Cisco proprietary whereas 802.1Q is an open standard. Cisco is
moving away from ISL, however. In fact, some of the newer equipment no
longer supports it, such as the Cat4000 switches.
Dot1Q adds less bits to the frame, but the way in which it adds them makes
it somewhat less efficient. ISL adds several more bits to ends of the
frame, making it easier to view the trunking info bits, but the higher
number of bits makes the MTU that much higher as well. Dot1Q doesn't have
such a pronounced effect on MTU as does ISL.
I typically use Dot1Q these days. Knowing that Cisco is moving away from
ISL and the fact that other vendor's equipment supports Dot1Q makes it a
more sensible choice for future compatibility.
Rik
""Lopez, Robert"" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>
> What are the differences between isl and 802.1q trunking. If I'm in a
total
> cisco switched environment, should I always use isl? What would be a
good
> reason to use 802.1q? Which one is more favored over the other?
>
> Robert
>
>
>
> Robert M. Lopez
> Network Planning
> Ann Arbor Data Center
> Pfizer Global Research & Development
>
>
>
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