Load Sharing Using Stp Path Cost - Cisco Catalyst 3120 Software Manual

Chapter 12 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, blocking different ports for different VLANs.
The VLANs keep the traffic separate and maintain redundancy in the event of a lost link.
In Figure
assigned:
•
•
•
•
Figure 12-5
VLANs 2
VLANs 8
Beginning in privileged EXEC mode, follow these steps to configure the network shown in
Command
Step 1 configure terminal
Step 2
interface gigabitethernet1/0/1
Step 3
switchport trunk encapsulation
{isl | dot1q | negotiate}
Step 4
switchport mode trunk
Step 5 exit
Step 6
Step 7
end
Step 8
show running-config
Step 9 show vlan
Step 10 configure terminal
OL-12247-01
12-5, Trunk ports 1 and 2 are configured as 100BASE-T ports. These VLAN path costs are
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
– 4 (path cost 30)
– 10 (path cost 19)
Switch B
Switch A
Trunk port 2
VLANs 8 – 10 (path cost 30)
VLANs 2 – 4 (path cost 19)
Purpose
Enter global configuration mode on Switch A.
Define the interface to be configured as a trunk, and enter interface
configuration mode.
Configure the port to support ISL or IEEE 802.1Q encapsulation. You
must configure each end of the link with the same encapsulation type.
Configure the port as a trunk port. The trunk defaults to ISL trunking.
Return to global configuration mode.
Repeat Steps 2 through 5 on a second interface in Switch A or in the
Switch A stack.
Return to privileged EXEC mode.
Verify your entries. In the display, make sure that the interfaces are
configured as trunk ports.
When the trunk links come up, Switch A receives the VTP information
from the other switches. Verify that Switch A has learned the VLAN
configuration.
Enter global configuration mode.
Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
Configuring VLAN Trunks
Figure 12-5:
12-27