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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Chapter 8 Configuring VLANs
Load Sharing Using STP
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 8-6
, 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 8-6
Load-Sharing Trunks with Traffic Distributed by Path Cost
Step 16
interface fa0/1
Enter interface configuration mode, and define the interface to set the STP
port priority.
Step 17
spanning-tree vlan 8 9 10
port-priority 10
Assign the port priority of 10 for VLANs 8, 9, and 10.
Step 18
end
Return to global configuration mode.
Step 19
interface fa0/2
Enter interface configuration mode, and define the interface to set the STP
port priority.
Step 20
spanning-tree vlan 3 4 5 6 port
priority 10
Assign the port priority of 10 for VLANs 3, 4, 5, and 6.
Step 21
exit
Return to privileged EXEC mode.
Step 22
show running-config
Verify your entries.
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)
