port priority in mst

The_guroo_2 · ‎01-11-2009

A B C D

A connected to B fa 0/1 fa 0/2 and D on fa 20/21

B is conected to C fa 0/1 fa0/2

C is conedted to D fa0/1 fa0/2

B is also conedted to D fa 20 fa21

D is conedted to A as well fa 20 and fa21

its a full redundant topolgy

i have 6 vlans swicth A is server and the rest is client

Vlan 234567

i have config mst (on all swicthes)

instance 1 234

instance 2 567

swicth A is root for instance 1

swicth D is root for instance 2

when i do sh spanning tree mst on switch on A

all ports are blocked expept fa0/1 which is connected to switch B

now i tried to config instance 1 on fa 20 and instance 2 on fa 21 (which is connedted to switch D)

i put the comand spanning tree mst 1 port-priority 200 on fa20 and same except instance 2 on fa21

after that when i do sh priority is been changed but the port is still in blocking mode why is that i even try to put cost but still port is in blocking mode

drolemc · ‎01-19-2009

Cisco IOS uses the port priority value when the LAN port is configured as an access port and uses VLAN port priority values when the LAN port is configured as a trunk port.

Try this example.

Router(config)# interface fastEthernet 20

Router(config-if)# spanning-tree mst 1 cost 1234567

Router(config-if)# spanning-tree mst 1 port-priority 240

Router(config-if)# ^Z

Router# show spanning-tree mst 1 interface fastEthernet 20