From: Asbjorn Hojmark (Asbjorn@xxxxxxxxxxx)
Date: Fri Mar 02 2001 - 20:25:04 GMT-3
> If I'm not mistaken dot1q was basically derived from the
> existing ISL standard but is platform independent.
Not really. Back then, there was quite a bit of debate on whether
it would be best to tag ethernet frames or encapsulate them. ISL
(encapsulation) is Ciscos pre-standard implementation of trunking
but as we all know, the 802.1Q standard turned out to be based on
tagging.
> I know one of the issues with dot1q as compared to ISL was the
> limitation of one Spanning-tree process per implementation,
> where ISL does an instance of STP per vlan.
The 802.1Q standard did support only one ST instance but Cisco
went ahead and implemented PVST on dot1q. So if you're using
Cisco gear, that's not an issue.
> I do believe however that 802.1q committee has a revision of
> another specific implementation (PVST+) that now support this
> function.
They're actually doing something a bit better than that, where
you can group multiple VLANs in the same spanning tree instance,
thus potentially lowering the load on the bridges as compared
to PVST. That work is in 802.1s which is currently in draft 8,
I believe.
Cisco already supports MISTP (Multiple-Instance Spanning Tree
Protocol) on Catalyst 6000 series switches from 6.1 and onwards.
-A
-- Heroes: Vint Cerf & Bob Kahn, Leonard Kleinrock, Robert Metcalfe Links : http://www.hojmark.org/networking/
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