Load Sharing Using Stp Path Cost - Cisco Catalyst 2950 Software Manual

Chapter 8 Configuring VLANs

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
follows:
•
•
•
•
Figure 8-5
VLANs 2 – 4 (path cost 30)
VLANs 8 – 10 (path cost 19)
Beginning in privileged EXEC mode, follow these steps to configure the network shown in
Command
Step 1 configure terminal
Step 2 interface fastethernet0/1
Step 3
switchport mode trunk
Step 4
end
Step 5
Step 6 show running-config
Step 7
show vlan
Step 8 configure terminal
Step 9
interface fastethernet0/1
Step 10
spanning-tree vlan 2 cost 30
78-11380-03
8-5, trunk ports 1 and 2 are 100BASE-T ports. The path costs for the VLANs are assigned as
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.
Load-Sharing Trunks with Traffic Distributed by Path Cost
Trunk port 1
Switch 2
Switch 1
Trunk port 2
VLANs 8 – 10 (path cost 30)
VLANs 2 – 4 (path cost 19)
Purpose
Enter global configuration mode on Switch 1.
Enter interface configuration mode, and define fastethernet 0/1 as
the interface to be configured as a trunk.
Configure the port as a trunk port.
Return to global configuration mode.
Repeat Steps 2 through 4 on Switch 1 interface fastethernet 0/2.
Verify your entries.
In the display, make sure that interfaces fastethernet 0/1 and
fastethernet 0/2 are configured as trunk ports.
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.
Enter global configuration mode.
Enter interface configuration mode, and define fastethernet 0/1 as
the interface to set the STP cost.
Set the spanning-tree path cost to 30 for VLAN 2.
Catalyst 2950 Desktop Switch Software Configuration Guide
Load Sharing Using STP
Figure 8-5:
8-27