From: kwasi-ccie@comcast.net
Date: Fri Apr 29 2005 - 13:57:34 GMT-3
Thanks, Brian.
Your comment "Just make sure that everyone in the same MST domain agrees on which VLANs are in which instance or you can create black holes or loops." answers my question.
-------------- Original message --------------
> The advantage of MST is that the STP instances are
> user-definable, where with CST there is only one instance, and with PVST
> there is one instance per VLAN. When you ask "do they have to be mapped
> to only one instance such as instance 1?", that is how CST works. With
> MST you can say for example VLANs 1-10 are in instance 1, VLANs 11-20
> are in instance 2, VLANs 21 - 30 are in instance 3... etc. Just make
> sure that everyone in the same MST domain agrees on which VLANs are in
> which instance or you can create black holes or loops.
>
> Design-wise what you should do is look for VLANs that you want
> to follow the same layer 2 forwarding path and put them in the same
> instance. This eliminates the unnecessary overhead of PVST, but gives
> you more control that just a common spanning-tree does.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
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>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > kwasi-ccie@comcast.net
> > Sent: Friday, April 29, 2005 9:40 AM
> > To: ccielab@groupstudy.com
> > Subject: Help understanding MST
> >
> > Hi:
> >
> > I am trying to understand how MST works. One aspect that I am not
> clear
> > on is the fact that for any switch to be part of an MST Region it must
> > have the same VLAN-to-Instance mapping, beside the same MST name and
> > version #.
> >
> > Does this mean all VLANs on a switch in an MST region can be mapped to
> > only one MST instance? For instance can I have VLAN 10 and VLAN 20
> (on an
> > MST switch in an MST region) mapped to say instance s 1 and 2,
> > respectively? Or do they have to be mapped to only one instance such
> as
> > instance 1?
> >
> > If I can only map multiple VLANs to only one instance, then what is
> the
> > need for having instances 1 - 15 for internal MST switches?
> >
> > I have read CCO but the examples are not clear enough for me on this
> > issue.
> >
> > Your comments are welcome.
> > Thanks.
> >
> >
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