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Chapter 7
Configuring Spanning Tree
Configuring the PVST+ Port Priority
You can configure the port priority of switch ports in PVST+ mode. The port with the lowest priority
value forwards frames for all VLANs. The possible port priority value is a multiple of 16 from 0–240.
The default is 32. If all ports have the same priority value, the port with the lowest port number forwards
frames.
To configure the PVST+ port priority for a port, perform this task in privileged mode:
Task
Step 1
Configure the PVST+ port priority for a
switch port.
Step 2
Verify the port priority setting.
This example shows how to configure the PVST+ port priority for a port:
Console> (enable) set spantree portpri 2/3 48
Bridge port
Console> (enable) show spantree 2/3
VLAN 1
Port
------------------------ ---- ------------- --------- ---- -------- ----------
1/1
1/2
2/1
2/2
2/3
2/4
This example shows that values that are not multiples of 16 (between the values of 0–63) are converted
to the nearest multiple of 16:
Console> (enable) set spantree portpri 2/3 2
Vlan port priority must be one of these numbers:0, 16, 32, 48, 64, 80,
96, 112, 128, 144,
160, 176, 192, 208, 224, 240
converting 2 to 0 nearest multiple of 16
Bridge port
Configuring the PVST+ Default Port Cost Mode
If any switch in your network is using a port speed of 10 Gb or over and the network is using PVST+
spanning-tree mode, all switches in the network must have the same path cost defaults. You can enter the
set spantree defaultcostmode command to force all VLANs that are associated with all the ports to have
the same port cost default set.
Two default port cost modes are available—short and long.
•
OL-8978-04
2/3 port priority set to 48.
.
.
.
Vlan Port-State
1
1
1
1
1
1
2/3 port priority set to 0.
The short mode has these parameters:
–
Portcost
Portvlancost (trunk ports only)
–
When UplinkFast is enabled, the actual cost is incremented by 3000
–
Command
set spantree portpri mod/port priority
show spantree mod/port
Cost
not-connected
not-connected
not-connected
100
not-connected
100
forwarding
19
not-connected
100
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Configuring PVST+ on the Switch
Prio Portfast Channel_id
4
32 disabled 0
4
32 disabled 0
32 disabled 0
32 disabled 0
48 disabled 0
32 disabled 0
7-29
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Troubleshooting
