Re: MSTP IST( MSTI0) vs MIST confusion

Hi Kid,

Yes Joe is spot on. M-Records contain the information about the root
priority, designated bridge priority, port priority and root path cost among
others using the extended TLV's for the specific instances which maps for
 various vlans.

IST also contain the same information for vlans which are not the part of
instances. MSTI's are again not a separate BPDU's . It is just been attached
with IST's

 To answer ur question more specifically about the contents in the MSTP
BPDu's, the major contents are the CIST Root Identifier , CIST Bridge ID,
CIST Regional Root ID, CIST Port ID and CIST External and Internal root
path cost. Inside each region in MSTP they have Regional Root and across the
boundaries they have CIST Root . Inside each region , they share the IST
which informs the entire logical topological information about the instances
and also the vlans which maps to that instances.

There is also field called as Remaining Hops (which is the maximum hops) in
the MSTP BPDU which states that a downstream switch should decrement the
hop count field on reception of IST BPDU. As soon as hop count becomes zero,
the information in BPDU is ignored, and the switch may start declaring
itself as a new IST root.

There is also a thing which should be understood in MSTP is IST Root is
equal to the CIST Regional Root.

CIST Root is the bridge that has the lowest Bridge ID among ALL regions.
This could be a bridge inside a region or a boundary switch in a region.

CIST Regional Root is a boundary switch elected for every region based on
the shortest external path cost to reach the CIST Root. Path cost is
calculated based on costs of the links connecting the regions, excluding the
internal regional paths.

I hope this will clear ur mind :)

On Wed, Sep 7, 2011 at 7:45 PM, Joe Astorino <joeastorino1982_at_gmail.com>wrote:

> MST does not carry the spanning-tree information for all the different
> MSTIs in a separate packet. So, what it does is send the spanning-tree
> characteristics for each MSTI in M-Records. The M-Records contain all that
> informatino per MSTI like port-priority, root path cost, etc
>
> HTH
>
>
> On Wed, Sep 7, 2011 at 9:45 AM, CCIE KID <eliteccie_at_gmail.com> wrote:
>
>> Thanks a lot hemanth .Gud explanation.
>>
>> One more question What does M-Record contain and wat r the contents in
>> IST
>> BPDU . What is the difference between the contents in M-Record and IST
>> BPDUs
>> ?
>>
>>
>>
>> On Wed, Sep 7, 2011 at 6:54 PM, HEMANTH RAJ <hemanthrj_at_gmail.com> wrote:
>>
>> > 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 MSTI s information in separate BPDUs, this
>> > information is attached into the IST s 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)
>> >>
>> >>
>> >> Blogs and organic groups at http://www.ccie.net
>> >>
>> >> _______________________________________________________________________
>> >> Subscription information may be found at:
>> >> http://www.groupstudy.com/list/CCIELab.html
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >
>> >
>> > --
>> > Problems arise because we talk,problems are not solved because we don't
>> > talk So good or bad talk to your affectionate one's freely.
>> >
>> > Yours Friendly,
>> > H P HEMANTH RAJ
>> > CCIE#28593 (R&S)
>> > Cisco Systems
>> >
>> >
>>
>>
>> --
>> With Warmest Regards,
>>
>> CCIE KID
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>>
>>
>>
>>
>>
>>
>
>
> --
> Regards,
>
> Joe Astorino
> CCIE #24347
> Blog: http://astorinonetworks.com
>
> "He not busy being born is busy dying" - Dylan
>
>

-- 
Problems arise because we talk,problems are not solved because we don't talk
So good or bad talk to your affectionate one's freely.
Yours Friendly,
H P HEMANTH RAJ
CCIE#28593 (R&S)
Cisco Systems
Blogs and organic groups at http://www.ccie.net