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Chapter 7
Configuring Spanning Tree
Configuring MISTP Port Cost
You can configure the port cost of switch ports. Ports with lower port costs are more likely to be chosen
to forward frames. Assign lower numbers to ports attached to faster media (such as full duplex) and
higher numbers to ports attached to slower media.The possible range is 1 to 65535. The default differs
for different media. Path cost is typically equal to 1000 ÷ LAN speed in megabits per second.
To configure the port cost for a port, perform this task in privileged mode:
Task
Step 1
Configure the port cost for a switch port.
Step 2
Verify the port cost setting.
This example shows how to configure the port instance priority on a MISTP instance and verify the
configuration:
Console> (enable) set spantree portcost 2/12 22222222
Spantree port 2/12 path cost set to 22222222.
Console> (enable) show spantree mistp-instance active
Instance 1
Spanning tree mode
Spanning tree type
Spanning tree instance enabled
Designated Root
Designated Root Priority
Designated Root Cost
Designated Root Port
VLANs mapped:
Root Max Age
Bridge ID MAC ADDR
Bridge ID Priority
VLANs mapped:
Bridge Max Age 20 sec
Port
------------------------ ---- ------------- --------- ---- -------- ----------
2/12
Console> (enable)
Configuring MISTP Port Priority
You can configure the port priority of switch ports. The port with the lowest priority value forwards
frames for all VLANs. The possible port priority value is 0 to 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:
Task
Step 1
Configure the port priority for a switch port.
Step 2
Verify the port priority setting.
78-12647-02
MISTP-PVST+
ieee
00-d0-00-4c-18-00
32769
0
none
6
20 sec
Hello Time 2
00-d0-00-4c-18-00
32769
6
Hello Time 2
Inst Port-State
1
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
Command
set spantree portcost mod_num/port_num cost
show spantree mistp-instance instance
[mod_num/port_num] active
(root priority: 32768, sys ID ext: 1)
sec
Forward Delay 15 sec
(bridge priority: 32768, sys ID ext: 1)
sec
Forward Delay 15 sec
Cost
forwarding
22222222
Command
set spantree portpri mod_num/port_num priority
[instance]
show spantree mistp-instance instance
[mod_num/port_num] active
Using MISTP-PVST+ or MISTP
Prio Portfast Channel_id
40 disabled 0
7-23
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