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| Sun Ethernet Fabric Operating System ### STP Administration Guide

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## Configure the Dynamic Path Cost

Note - If the path cost is already configured for a CIST or RSTP interface, this procedure has no effect on such ports. If the cost has been configured previously for an MST instance on a particular interface, this command has no effect on that instance in the specified interface. The path cost of all the other instances on the same interface are calculated dynamically.

1. View the spanning tree configuration before configuring the dynamic path cost.
   1. In switch 1, type.

          SEFOS# show spanning-tree

          Root Id         Priority   32768
                          Address    00:01:02:03:04:01
                          Cost       0
                          Port       0 [0]
                          This bridge is the root
                         Max age 20 Sec, forward delay 15 Sec
                          Hello Time is 2 Sec
          MST00
          Spanning tree Protocol Enabled.
          MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
          Bridge Id       Priority  32768
                          Address  00:01:02:03:04:01
                         Max age is 20 sec, forward delay is 15 sec
                          Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is Disabled
          Name      Role         State        Cost     Prio   Type
          ----      ----         -----        ----     ----   ------
          Ex0/1     Designated   Forwarding   20000   128    SharedLan
          Ex0/2     Designated   Forwarding   20000   128    SharedLan

   2. In switch 2, type.

          SEFOS# show spanning-tree

          Root Id         Priority   32768
                          Address    00:01:02:03:04:01
                          Cost       200000
                          Port       1 [Ex0/1]
                         Max age 20 Sec, forward delay 15 Sec
                          Hello Time is 2 Sec

          MST00
          Spanning tree Protocol Enabled.
          MST00 is executing the mstp compatible Multiple Spanning Tree Protocol
          Bridge Id       Priority  32768
                          Address  00:02:02:03:04:01
                         Max age is 20 sec, forward delay is 15 sec
                          Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is Disabled
          Name      Role         State        Cost     Prio   Type
          ----      ----         -----        ----     ----   ------
          Ex0/1     Root         Forwarding   20000   128    SharedLan
          Ex0/2     Alternate    Discarding   20000   128    SharedLan

2. Configure the dynamic path cost in switch 2.

       SEFOS# configure terminal
       SEFOS(config)# spanning-tree pathcost dynamic

3. Reduce the speed of the `extreme-ethernet 0/1` interface to 10 Mbps in switch 2.

       SEFOS(config)# interface extreme-ethernet 0/1
       SEFOS(config-if)# no negotiation
       SEFOS(config-if)# speed 10

4. View the spanning tree details in switch 2.

       SEFOS# show spanning-tree

       Root Id         Priority   32768                Address    00:01:02:03:04:01                Cost       200000                Port       2 [Ex0/2]               Max age 20 Sec, forward delay 15 Sec
                       Hello Time is 2 Sec MST00Spanning tree Protocol Enabled.MST00 is executing the mstp compatible Multiple Spanning Tree ProtocolBridge Id       Priority  32768                Address  00:02:02:03:04:01                Max age is 20 sec, forward delay is 15 sec
                       Hello Time is 2 sec                Dynamic Path Cost is Disabled                Dynamic Path Cost Lag-Speed Change is DisabledName      Role         State        Cost     Prio   Type----      ----         -----        ----     ----   ------Ex0/1     Alternate    Discarding   2000000  128    P2P    Ex0/2     Root         Forwarding   20000    128   P2P

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