Re: MSTP IST( MSTI0) vs MIST confusion

Petr from INE has a very nice article on it here
http://blog.ine.com/2010/02/22/understanding-mstp/#MSTI_TO_CIST

On Wed, Sep 7, 2011 at 3:58 PM, CCIE KID <eliteccie_at_gmail.com> wrote:

> Thanks a lot Hemanth Got the point completely.
> Do u have any scenarios or case studies which describes MSTP in depth.
>
>
> On Wed, Sep 7, 2011 at 11:49 PM, HEMANTH RAJ <hemanthrj_at_gmail.com> wrote:
>
>> 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:
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>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >
>>>> >
>>>> > --
>>>> > 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
>>
>>
>
>
> --
> With Warmest Regards,
>
> CCIE KID
> IN PURSUIT OF CCIE
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net