From: Scott Morris (smorris@xxxxxxxxxxxxxx)
Date: Sun Mar 04 2001 - 19:06:42 GMT-3
Ummm... I may be off on this, but unless something's changed....
802.1q still only has CST, or "common spanning tree", which is one per
network, period (not one per VLAN). ISL has the PVST, or "per VLAN spannint
tree".
Cisco specifically has made some enhancments, calling it PVST+, which on
CISCO equipment running 802.1q will give you per vlan spanning trees. It
does this by encapsulating the BPDU's into a multicast packet, so any
non-Cisco switches will flood it by default.
But as far as I am aware, 802.1q is still CST only as a "world-wide"
standard....
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Troy Allen McCarty
Sent: Saturday, March 03, 2001 11:11 PM
To: David C Prall; ccielab@groupstudy.com
Subject: Re: Re[2]: ISL Trunking vs dot1q
My understanding was that the benefit of ISL over dot1q was the per-vlan
instance of spanning-tree. Subsequently, dot1q was improved to allow
per-vlan instances of spanning-tree; therefore, a Cisco proprietary protocol
(ISL) was no longer needed.
Any comments?
Regards,
Troy McCarty
CCIE #6967
At 08:30 PM 3/3/2001 -0500, you wrote:
>----- Original Message -----
>From: "Chuck Larrieu" <chuck@cl.cncdsl.com>
>> According to the most recent product quick reference guide ( Aug 2000 )
>>
>> The 4003 and 4006 both support 802.1Q
>>
>> Both also support ISL through the Layer 3 module, but apparently not
>without
>> that module in place. ( WS-X4232-L3= )
>>
>> I seem to remember rumblings around work about this "surprise" with a
>major
>> customer / installation one of the groups was working on.
>>
>> Chuck
>>
>
>The layer 3 blade supports ISL on the 2 - Gigabit ports off the front.
These
>are the only ports on a Catalyst 4000 that support ISL. The 2 Gigabit ports
>off the back I am not sure of since you are connecting them directly to the
>backplane.
>
>David
>
>David C Prall dcp@dcptech.com http://dcp.dcptech.com
>
>
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