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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 7 Configuring Spanning Tree
Configuring PVST+ on the Switch
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:
This example shows how to configure the PVST+ port priority for a port:
Console> (enable)
set spantree portpri 2/3 48
Bridge port 2/3 port priority set to 48.
Console> (enable)
show spantree 2/3
VLAN 1
.
.
.
Port Vlan Port-State Cost Prio Portfast Channel_id
------------------------ ---- ------------- --------- ---- -------- ----------
1/1 1 not-connected 4 32 disabled 0
1/2 1 not-connected 4 32 disabled 0
2/1 1 not-connected 100 32 disabled 0
2/2 1 not-connected 100 32 disabled 0
2/3 1 forwarding 19 48 disabled 0
2/4 1 not-connected 100 32 disabled 0
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 2/3 port priority set to 0.
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.
•
The short mode has these parameters:
–
Portcost
–
Portvlancost (trunk ports only)
–
When UplinkFast is enabled, the actual cost is incremented by 3000
Task
Command
Step 1
Configure the PVST+ port priority for a
switch port.
set spantree portpri
mod/port
priority
Step 2
Verify the port priority setting.
show spantree
mod
/
port