Load Sharing Using Stp Path Cost - Cisco 2950 - Catalyst Switch Configuration Manual

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. 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
as follows:
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•
•
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Figure 17-4 Load-Sharing Trunks with Traffic Distributed by Path Cost
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 fastethernet 0/1
Step 3 switchport mode trunk
Step 4 exit
Step 5
Step 6
end
Step 7 show running-config
Step 8 show vlan
Step 9
configure terminal
Step 10
interface fastethernet 0/1
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
17-24
17-4, Trunk ports 1 and 2 are 100BASE-T ports. The path costs for the VLANs 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.
Trunk port 1
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.
Enter interface configuration mode, and define Fast Ethernet port 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 A interface Fast Ethernet 0/2.
Return to privileged EXEC mode.
Verify your entries.
In the display, make sure that interfaces Fast Ethernet 0/1 and Fast
Ethernet 0/2 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.
Enter interface configuration mode, and define Fast Ethernet port 0/1 as
the interface to set the STP cost.
Chapter 17 Configuring VLANs
Figure 17-4:
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