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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
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Chapter 7 Configuring Spanning Tree
Configuring MST
Configuring the MST Port Priority
You can configure the port priority of ports. The port with the lowest priority value forwards frames for
all VLANs. The possible port priority value is from 0–63; the default is 32. If all ports have the same
priority value, the port with the lowest port number forwards 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 BDRY 10000 30 2-20
2 forwarding BDRY 10000 30 21-30
3 forwarding BDRY 10000 30 31-40
4 forwarding BDRY 10000 30 41-50
Console> (enable)
Configuring the MST Port Instance Cost
You can configure the port instance cost for an instance of MST. Ports with a lower instance cost are
more likely to be chosen to forward frames. You should assign lower numbers to ports that are attached
to faster media (such as full duplex) and higher numbers to ports that are attached to slower media. The
default cost differs for different media. The possible value for port instance cost is from 1–268,435,456.
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 6/1 cost 5000 mst 4
Port 6/1 MST Instances 0-3,5-15 have path cost 10000.
Port 6/1 MST Instances 4 have path cost 5000.
Console> (enable)
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 instances on a port. show spantree portinstancecost mod/port
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