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Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 14 Configuring VLANs
Configuring VLAN Trunks
Load Sharing Using STP Path Cost
You can configure parallel trunks to share VLAN traffic by setting different path costs on a trunk and
associating the path costs with different sets of VLANs. The VLANs keep the traffic separate. Because
no loops exist, STP does not disable the ports, and redundancy is maintained in the event of a lost link.
In Figure 14-4, Trunk ports 1 and 2 are 100BASE-T ports. The path costs for the VLANs are assigned
as follows:
• VLANs 2 through 4 are assigned a path cost of 30 on Trunk port 1.
• VLANs 8 through 10 retain the default 100BASE-T path cost on Trunk port 1 of 19.
• VLANs 8 through 10 are assigned a path cost of 30 on Trunk port 2.
• VLANs 2 through 4 retain the default 100BASE-T path cost on Trunk port 2 of 19.
Figure 14-4 Load-Sharing Trunks with Traffic Distributed by Path Cost
Step 17
spanning-tree vlan 8 port-priority 10 Assign the port priority of 10 for VLAN 8.
Step 18
spanning-tree vlan 9 port-priority 10 Assign the port priority of 10 for VLAN 9.
Step 19
spanning-tree vlan 10 port-priority 10 Assign the port priority of 10 for VLAN 10.
Step 20
exit Return to global configuration mode.
Step 21
interface fastethernet0/2 Enter interface configuration mode, and define the interface to set the
STP port priority.
Step 22
spanning-tree vlan 3 port-priority 10 Assign the port priority of 10 for VLAN 3.
Step 23
spanning-tree vlan 4 port-priority 10 Assign the port priority of 10 for VLAN 4.
Step 24
spanning-tree vlan 5 port-priority 10 Assign the port priority of 10 for VLAN 5.
Step 25
spanning-tree vlan 6 port-priority 10 Assign the port priority of 10 for VLAN 6.
Step 26
end Return to privileged EXEC mode.
Step 27
show running-config Verify your entries.
Step 28
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
16591
Switch 1
Switch 2
Trunk port 1
VLANs 2 – 4 (path cost 30)
VLANs 8 – 10 (path cost 19)
Trunk port 2
VLANs 8 – 10 (path cost 30)
VLANs 2 – 4 (path cost 19)