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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 14 Configuring VLA Ns Configurin g VLAN Trunks

Load Sharing Using STP Path Cost

You can co nfigure paralle l trunks to sha re VLAN traffic by setting di fferent 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 po rts, a nd redu nda ncy is mainta ined in the event of a lost li nk.
In Figure 14-4, Trunk ports 1 and 2 are 100 BASE-T ports . The path costs for the VLANs are assi gned
as fo l lows:
•VLANs 2 t hroug h 4 a re a ssign ed a pa th co st of 3 0 o n Trunk port 1 .
•VLANs 8 t hr ough 1 0 re tain th e de fault 100BASE-T pat h cost o n Trunk port 1 of 1 9.
•VLANs 8 t hroug h 1 0 ar e assig ned a p ath co st o f 30 on Trunk port 2.
•VLANs 2 t hroug h 4 r etai n the default 1 00BASE-T p ath co st 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 po rt priorit y of 10 for VLA N 8.
Step 18 spanning-tree vlan 9 port-priority 10 Assign the po rt priorit y of 10 for VLA N 9.
Step 19 spanning-t ree vlan 10 port-priority 10 Assign the po rt priorit y of 10 for VLA N 10.
Step 20 exit Return to global configuration mod e.
Step 21 int erf a ce f as t et hern et0/ 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 po rt priorit y of 10 for VLA N 3.
Step 23 spanning-tree vlan 4 port-priority 10 Assign the po rt priorit y of 10 for VLA N 4.
Step 24 spanning-tree vlan 5 port-priority 10 Assign the po rt priorit y of 10 for VLA N 5.
Step 25 spanning-tree vlan 6 port-priority 10 Assign the po rt priorit y of 10 for VLA N 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)