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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 16 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 16-4, 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 16-4 Load-Sharing Trunks with Traffic Distributed by Path Cost
Beginning in privileged EXEC mode, follow these steps to configure the network shown in Figure 16-4:
Step 18
spanning-tree vlan 10 port-priority 16 Assign the port priority of 16 for VLAN 10.
Step 19
exit Return to global configuration mode.
Step 20
interface Enter interface configuration mode, and define the interface to set the
STP port priority.
Step 21
spanning-tree vlan 3-6 port-priority 16 Assign the port priority of 16 for VLANs 3 through 6.
Step 22
end Return to privileged EXEC mode.
Step 23
show running-config Verify your entries.
Step 24
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
90573
Switch A
Switch B
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)
Command Purpose
Step 1
configure terminal Enter global configuration mode on Switch A.
Step 2
interface Enter interface configuration mode, and define as the interface to be
configured as a trunk.
Step 3
switchport mode trunk Configure the port as a trunk port.
Step 4
exit Return to global configuration mode.