Re: MSTP IST( MSTI0) vs MIST confusion

Hi kid,

IST is nothing but ur MST Instance 0 which mainly serves the purpose of
distributing STP topology information for MST Instances. IST has a root
bridge, elected based on the lowest Bridge ID (Bridge Priority + MAC
address). The situation changes with multiple MSTP regions in the network.

By default, all VLANs are mapped to the IST .Other MSTP instances could be
enabled and they are referred to as Multiple Spanning Tree Instances
(MSTIs). Every MSTI assign its own priorities to the switches and use its
own link costs to come up with a private logical topology which is separate
from IST

Since MSTP does not send MSTIs information in separate BPDUs, this
information is attached into the ISTs BPDUs using special M-Record fields.
I think these M-Records are one for every active MST Instances. They have
extended TLVs to do that I guess if i remember correctly.

I hope this helps u

On Wed, Sep 7, 2011 at 2:33 PM, CCIE KID <eliteccie_at_gmail.com> wrote:

> Hi fellas,
>
> I am reading MSTP and i came across two terminologies IST and MIST.
> IST is used to send all the BPDU related information which is all the
> information regarding which VLANS mapped to which instances and to maintain
> consistency check on all the switches.
> Now there is a line which states " *MSTI information is attached to IST *"
> What does MSTI carry and why does it use IST for that
> Correct me if i am wrong in understanding the logic.
>
> I have a confusion regarding Internal Spanning tree (IST) aka MST Instance
> 0 and Multiple Intances of Spanning tree(MIST). Can some point me what is
> the difference between IST and MST ?
>
> --
> With Warmest Regards,
>
> CCIE KID
> CCIE#29222 ( SECURITY)
>
>
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