The text below is taken from the following URL:
http://www.cisco.com/warp/public/473/27.html
Spanning Tree Consideration
802.1q standard is more than just a tagging mechanism. It also defines a
unique spanning tree instance running on the native VLAN for all the VLANs
in the network. Such a Mono Spanning Tree(MST) network lacks some
flexibility compared to a Per VLAN Spanning Tree network (PVST) that runs
one instance of Spanning Tree Protocol (STP) per VLAN. Cisco developed PVST+
to allow running several STP instances (even over a 802.1q network) by using
a tunneling mechanism. Although beyond the scope of this document, it can be
briefly described as utilizing a Cisco device to connect a MST zone
(typically another vendor's 802.1q-based network) to a PVST zone (typically
a Cisco ISL based network). There is no specific configuration to enter in
order to achieve this. Ideally, a mixed environment should look like the
following diagram:
Brant I. Stevens
Internetwork Solutions Engineer
Thrupoint, Inc.
545 Fifth Avenue, 14th Floor
New York, NY. 10017
646-562-6540
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Erick B.
Sent: Friday, February 02, 2001 12:09 AM
To: Chris Supino; Fred Danson
Cc: [EMAIL PROTECTED]
Subject: RE: ISL vs. 802.1Q
Other vendors (Nortel/Bay) support multiple spanning
tree groups on 802.1q as well. I think each
implementation is propiertary at moment. I heard
something about the IEEE working on a updated 802.1q
standard but I don't know where that stands today.
Anyone know?
I haven't tried Cisco 802.1q w/multiple VLANs and STGs
to a Nortel/Bay box so can't comment on how Cisco's
per-vlan stg extension effects the trunk link; I'll
have to give it a try to see what happens.
--- Chris Supino <[EMAIL PROTECTED]> wrote:
> I would suspect that non-cisco devices would
> probably ignore the additional
> info(bits?). I really didn't press the lecturer as
> this was an off-topic
> discussion. You do have an interesting point,
> though.
>
> -----Original Message-----
> From: Fred Danson [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, February 01, 2001 1:57 PM
> To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: RE: ISL vs. 802.1Q
>
> If Cisco were to add-on to dot1q, how would it be
> able to communicate with
> other non-Cisco routers using 802.1q?
>
>
> >From: Chris Supino <[EMAIL PROTECTED]>
> >Reply-To: Chris Supino <[EMAIL PROTECTED]>
> >To: Jun Pati <[EMAIL PROTECTED]>,
> [EMAIL PROTECTED]
> >Subject: RE: ISL vs. 802.1Q
> >Date: Wed, 31 Jan 2001 21:04:30 -0500
> >
> >Jun,
> >
> >Used to be that ISL supported a spanning-tree per
> VLAN, where Dot1q
> >supported only a single spanning-tree. I was told
> at a seminar recently
> >that
> >Cisco has expanded the capabilities of their
> implementation of Dot1q, and
> >it
> >is now almost as fully featured as ISL, including
> supporting a
> >spanning-tree
> >per vlan. ISL is being phased out.
> >
> >Christopher Supino
> >MCSE, MCP+I, CCNA, CNA Netware 5, Compaq ASE
> >Senior Systems Engineer
> >TransNet Corp.
> >
> >-----Original Message-----
> >From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of
> >Jun Pati
> >Sent: Wednesday, January 31, 2001 7:29 PM
> >To: [EMAIL PROTECTED]
> >Subject: ISL vs. 802.1Q
> >
> >
> >What is the advantage of using ISL on an all-Cisco
> network compared to
> >dot1Q
> >aside from being able to handle frames larger than
> the ethernet mtu.
> >
> >
> >_________________________________
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>
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