13-27
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 13 Configuring VLANs
Configuring VLAN Trunks
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:
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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 gigabitethernet1/0/1 Define the interface to be configured as a trunk, and enter interface
configuration mode.
Step 3
switchport trunk encapsulation
{isl | dot1q | negotiate}
Configure the port to support ISL or IEEE 802.1Q encapsulation. You
must configure each end of the link with the same encapsulation type.
Step 4
switchport mode trunk Configure the port as a trunk port. The trunk defaults to ISL trunking.
Step 5
exit Return to global configuration mode.
Step 6
Repeat Steps 2 through 5 on a second interface in the Switch A stack.
Step 7
end Return to privileged EXEC mode.
Step 8
show running-config Verify your entries. In the display, make sure that the interfaces are
configured as trunk ports.
Step 9
show vlan 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.
Step 10
configure terminal Enter global configuration mode.
Step 11
interface gigabitethernet1/0/1 Define the interface on which to set the STP cost, and enter interface
configuration mode.
Step 12
spanning-tree vlan 2-4 cost 30 Set the spanning-tree path cost to 30 for VLANs 2 through 4.
Step 13
end Return to global configuration mode.
Step 14
Repeat Steps 9 through 13 on the other configured trunk interface on
Switch A, and set the spanning-tree path cost to 30 for VLANs 8, 9, and
10.
Step 15
exit Return to privileged EXEC mode.
Step 16
show running-config Verify your entries. In the display, verify that the path costs are set
correctly for both trunk interfaces.
Step 17
copy running-config startup-config (Optional) Save your entries in the configuration file.
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