Cisco Systems 3560 Load Sharing Using STP Path Cost

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Catalyst 3560 Switch Software Configuration Guide
OL-8553-06
Chapter 13 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, blocking different ports for different VLANs.
The VLANs keep the traffic separate and maintain redundancy in the event of a lost link.
In Figure 13-4, Trunk ports 1 and 2 are configured as 100BASE-T ports. These VLAN path costs are
assigned:
• 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 13-4 Load-Sharing Trunks with Traffic Distributed by Path Cost
Beginning in privileged EXEC mode, follow these steps to configure the network shown in Figure 13-4:
Step 17 interface gigabitethernet 0/1 Define the interface to set the STP port priority, and enter interface
configuration mode.
Step 18 spanning-tree vlan 8-10 port-priority 16 Assign the port priority of 16 for VLANs 8 through 10.
Step 19 exit Return to global configuration mode.
Step 20 interface gigabitethernet0/2 Define the interface to set the STP port priority, and enter interface
configuration mode.
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 gigabitethernet0/1 Define the interface to be configured as a trunk, and enter interface
configuration mode.