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Catalyst 3750 Metro Switch Software Configuration Guide
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Chapter 10 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 10-4, 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.
Step 8
interface gigabitethernet1/ 0/1 Enter interface configuration mode, and define Gigabit Ethernet
port 1 as the interface to be configured as a trunk.
Step 9
switchport trunk encapsulation {isl |
dot1q | negotiate}
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.
Step 10
switchport mode trunk Configure the port as a trunk port.
Step 11
end Return to privileged EXEC mode.
Step 12
show interfaces gigabitethernet1/ 0/1
switchport
Verify the VLAN configuration.
Step 13
Repeat Steps 7 through 11 on Switch A for a second interface in the
switch.
Step 14
Repeat Steps 7 through 11 on Switch B to configure the trunk ports
that connect to the trunk ports configured on Switch A.
Step 15
show vlan 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.
Step 16
configure terminal Enter global configuration mode on Switch A.
Step 17
interface gigabitethernet1/ 0/1 Enter interface configuration mode, and define the interface to set the
STP port priority.
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 gigabitethernet1/0/2 Enter interface configuration mode, and define the interface to set the
STP port priority.
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
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