Load Sharing Using Stp Path Cost - Cisco Catalyst 3750 Software Configuration Manual

Configuring VLAN Trunks
Command
Step 8 interface gigabitethernet1/ 0/1
Step 9
switchport trunk encapsulation {isl |
dot1q | negotiate}
Step 10
switchport mode trunk
Step 11
end
Step 12 show interfaces gigabitethernet1/ 0/1
switchport
Step 13
Step 14
Step 15
show vlan
Step 16
configure terminal
Step 17
interface gigabitethernet1/ 0/1
Step 18 spanning-tree vlan 8-10 port-priority 16
Step 19 exit
Step 20
interface gigabitethernet1/0/2
Step 21
spanning-tree vlan 3-6 port-priority 16
Step 22 end
Step 23 show running-config
Step 24
copy running-config startup-config

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:
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Catalyst 3750 Metro Switch Software Configuration Guide
10-26
10-4, 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.
Purpose
Enter interface configuration mode, and define Gigabit Ethernet
port 1 as the interface to be configured as a trunk.
Configure the port to support ISL or 802.1Q encapsulation or to
negotiate with the neighboring interface. You must configure each
end of the link with the same encapsulation type.
Configure the port as a trunk port.
Return to privileged EXEC mode.
Verify the VLAN configuration.
Repeat Steps 7 through 11 on Switch A for a second interface in the
switch.
Repeat Steps 7 through 11 on Switch B to configure the trunk ports
that connect to the trunk ports configured on Switch A.
When the trunk links come up, VTP passes the VTP and VLAN
information to Switch B. Verify that Switch B has learned the VLAN
configuration.
Enter global configuration mode on Switch A.
Enter interface configuration mode, and define the interface to set the
STP port priority.
Assign the port priority of 16 for VLANs 8 through 10.
Return to global configuration mode.
Enter interface configuration mode, and define the interface to set the
STP port priority.
Assign the port priority of 16 for VLANs 3 through 6.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 10 Configuring VLANs
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