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You can set the port
priority for a port on a per-VLAN basis. The port with the lowest
priority value for a specific VLAN forwards frames for that VLAN. If
all ports have the same priority value for a particular VLAN, the
port with the lowest port number forwards frames for that VLAN.
This command is useful
for distributing data across parallel paths. By default, if there is
a parallel connection between two devices, Spanning Tree will block
one of the links. Traffic from all VLANs would travel on one link,
and one link would be used only as backup.
By changing the port
priority for a specific group of VLANs, you can distribute the VLANs
across the two links. In the example in Figure ,
Port 1/2 will forward for VLANs 100 to 105 and block for VLANs 106
to 110. The opposing Port 1/1 will forward for VLANs 106 to 110 and
block for VLANs 100 to 105.
To change the port VLAN
priority for a port on a set command-based switch, enter the set
spantree portvlanpri mod-num/port-num priority [vlans]
in privileged mode. Verify the port-VLAN priority setting by
entering the show spantree
[mod-num/port-num] command
in privileged mode. 
To change the port
priority on a Cisco IOS command-based switch, you can simply enter
the spanning-tree vlan
[stp-list] port-priority port-priority
command in interface configuration mode. The example in Figure
illustrates the use of this command by setting the interface
FastEthernet 0/3 with a priority of 10 for VLANs 1-10. This command
is verified by using the show
spanning-tree command.
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Interactive
Lab Activity (Flash,
260 kB) |
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In
this activity, you will learn how to configure
a Catalyst 4000 to become the root bridge for
the network. |
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