MST urgent help needed

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Jan 11th, 2009
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guys i have four swicthes all are connected to each other....MST is running and i have two instances.....swicth A and is root for instance 1 and swicth B is instance for instance 2......now th eport between A and B is 10 and 12......i want that odd vlans shd go on 12 and even vlan shd go on 10....as instance 1 has even vlans and instance two has odd vlans....i went to port 10 of both swicth it is in blocking state....i put the command spanning tree mst 1 port priority 16 on bith end....the prority chages on the swicth i can see that but still its in blocking state why is that........what is bound port.....now the strange thing is when i do shd spanning tree mst it shows me mst 0 has root port the other two instances have same port but its in boundr can someone please help me i tried cost as well but ports are still in blocking state

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Giuseppe Larosa Sun, 01/11/2009 - 04:55
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Hello Khan,

use the following doc as a reference


http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/spantree.html


have you configured the same MST region name, revision number, vlans to instances mappings on all routers manually ?

These parameters are not propagated automatically but need to be configured and updated on all devices when needed.


Do all the switches agree on root bridge-id for IST and other instances ?



Hope to help

Giuseppe


The_guroo_2 Sun, 01/11/2009 - 05:11
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Giuseppe

its all same same revision no same name in mst config same vtp domain same everything and i have been to this link....didnt help me my question remains still stands.....why its not coming in forwarding state....on switch A i have config instance 1 as root and on D instance 2 as root and after that verified that as well....so there is no point that they are not root for those instances.......can you please help me as i am going nuts




Giuseppe Larosa Sun, 01/11/2009 - 05:21
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Hello Khan,

in MST the actual BPDUs sent on the wire are those of IST (instance 0) so you need:

to have at least one vlan associated to instance 0

to have one vlan associated to instance 0 permitted and in forwarding state on every trunk port.


the data for additonal MST instances are carried as fields in IST BPDUs


if you like being a lab setup feel free to post your config of the four switches.


Hope to help

Giuseppe


The_guroo_2 Sun, 01/11/2009 - 05:25
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there is a vlan which is default one i mean vlan 1 is in mst0.


all i am saying is switch A is a root for instance 1 and swicth is root for instance 2


now on switch A when i put port priority which is a trunk connecting switch D why the port is still in blocking state??? thanks as usual

Giuseppe Larosa Sun, 01/11/2009 - 11:49
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Hello Khan,

post the configuration and


sh spanning-tree interface typex/y


sh int type x/y switchport


is Vlan1 permitted on the trunk ?


Hope to help

Giuseppe


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