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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 7 Configuring Spanning Tree
Configuring Multiple Spanning Tree on the Switch
Configuring the MST Port Priority
You can configure the port priority of ports. The port with the lowest priority value forwards the frames
for all VLANs. The possible port priority value is a multiple of 16 from 0–240. The default is 32. If all
the ports have the same priority value, the port with the lowest port number forwards the frames.
To configure the port priority for a port, perform this task in privileged mode:
This example shows how to configure the port priority and verify the configuration:
Console> (enable) set spantree portpri 6/1 30 mst
Bridge port 6/1 port priority set to 30.
Console> (enable)
Console> (enable) show spantree mst 6/1
Edge Port: No, (Configured) Default
Link Type: P2P, (Configured) Auto
Port Guard: Default
Boundary: Yes (PVST)
Inst State Role Cost Prio VLANs
---- ------------- ---- --------- ---------------------------------------
0 forwarding ROOT 10000 30 1
1 forwarding MSTR 10000 30 2-20
2 forwarding MSTR 10000 30 21-30
3 forwarding MSTR 10000 30 31-40
4 forwarding MSTR 10000 30 41-50
Console> (enable)
Configuring the MST Port Instance Cost
You can configure the port instance cost for an instance of MST. The ports with a lower instance cost are
more likely to be chosen to forward frames. You should assign lower numbers to the ports that are
attached to faster media (such as full duplex) and higher numbers to the ports that are attached to slower
media. The default cost differs for different media. The possible value for the port instance cost is
1–268435456.
You can assign a different port instance cost for the instances within a trunk port.
To configure the port instance cost for a port, perform this task in privileged mode:
This example shows how to configure the MST port instance cost on a port:
Console> (enable) set spantree portinstancecost 4/1 cost 5000 mst 4
Command successful. Modified port 4/1 configuration:
Cost Instances
Task Command
Step 1
Configure the MST port priority for a port. set spantree portpri mod/port priority [mst]
Step 2
Verify the port priority setting. show spantree mst [instance | mod/port]
Task Command
Step 1
Configure the MST port instance cost on a
port.
set spantree portinstancecost mod/port [cost cost] mst
[instances]
Step 2
Verify the path cost for the MST instances
on a port.
show spantree portinstancecost mod/port mst
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