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Catalyst 2950 Desktop Switch 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 8-5, 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.
• VLANs8through10areassignedapathcostof30ontrunkport2.
• VLANs 2 through 4 retain the default 100BASE-T path cost on trunk port 2 of 19.
Figure 8-5 Load-Sharing Trunks with Traffic Distributed by Path Cost
Beginning in privileged EXEC mode, follow these steps to configure the network shown in Figure 8-5:
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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)
Command Purpose
Step 1
configure terminal Enter global configuration mode on Switch 1.
Step 2
interface fastethernet0/1 Enter interface configuration mode, and define fastethernet 0/1 as
the interface to be configured as a trunk.
Step 3
switchport mode trunk Configure the port as a trunk port.
Step 4
end Return to global configuration mode.
Step 5
Repeat Steps 2 through 4 on Switch 1 interface fastethernet 0/2.
Step 6
show running-config Verify your entries.
In the display, make sure that interfaces fastethernet 0/1 and
fastethernet 0/2 are configured as trunk ports.
Step 7
show vlan When the trunk links come up, Switch 1 receives the VTP
information from the other switches. Verify that Switch 1 has
learned the VLAN configuration.
Step 8
configure terminal Enter global configuration mode.
Step 9
interface fastethernet0/1 Enter interface configuration mode, and define fastethernet 0/1 as
the interface to set the STP cost.
Step 10
spanning-tree vlan 2 cost 30 Setthespanning-treepathcostto30forVLAN2.
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