Re: Cisco Spanning Tree Mode for CST

Hi,

Like Marko said, you can use MST with a single CIST instance. This one
will automatically interwork with CST, but the CST region would see
the MST region as a single pseudo-bridge. You may also use PVST+
(which is implemented in virtually any Cisco switch) as this
implementation was specifically made to interoperate PVST with CST. It
is important to note though, that only VLAN1 STP is joined with the
CST - all other VLAN instances are transparently tunneled over the STP
domain, treating it as a "shared" link. This tunneling procedure also
implies that PVST+ timers should be "slightly" higher than CST (VLAN1)
timers, to allow for the "transport" domain to converge before the
overlay STP instances. However, in most cases that difference could be
ignored, unless you have complex meshy CST L2 domains.

HTH,

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
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2010/3/15 Marko Milivojevic <markom_at_ipexpert.com>:
> On Tue, Mar 16, 2010 at 02:14, Vincent Tay <vtay.75_at_gmail.com> wrote:
>> Hi Gurus,
>>
>> I have a practical issue with my network enviroment. As we are using a lot
>> of legacy switches, is there a way to configure Cisco switch to run purely
>> CST mode?
>
> Yes and no. MST instance 0 will talk to CST nicely.
>
> --
> Marko Milivojevic - CCIE #18427
> Senior Technical Instructor - IPexpert
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