11-7
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
—
Release 8.1
78-15486-01
Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
Configuring a Trunk Link
Note
When you first configure a port as a trunk, the set trunk command always adds all VLANs to the allowed
VLAN list for the trunk, even if you specify a VLAN range (any specified VLAN range is ignored). To
modify the allowed VLANs list, use the clear trunk and set trunk commands to specify the allowed
VLANs.
To define the allowed VLAN list for a trunk port, perform this task in privileged mode:
This example shows how to define the allowed VLANs list for trunk port 1/1 to allow VLANs 10, 20,
and VLAN 100, and how to verify the allowed VLAN list for the trunk:
Console> (enable) set trunk 1/1 10,20,100
Adding vlans 10, 20 to allowed list.
Port(s) 1/1 allowed vlans modified to 10,20,100,1002,1003,1004,1005.
Console> (enable) clear trunk 1/1 1-9,11-19,21-99,101-1001
Removing Vlan(s) 1-9,11-19,21-99,101-100 from allowed list.
Port 1/1 allowed vlans modified to 10,20,100.
Console> (enable) show trunk 1/1
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 desirable dot1q
trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/1 1,10,20,100
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/1
1,10,20,100
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/1
1,10,20,100
Console> (enable)
Disabling a Trunk Port
To explicitly turn off trunking on a port, perform this task in privileged mode:
Task
Command
Step 1
(Optional) Add specific VLANs to the allowed VLANs list
for a trunk.
set trunk mod_num/port_num vlans
Step 2
Remove VLANs from the allowed VLANs list for a trunk. clear trunk mod_num/port_num vlans
Step 3
Verify the allowed VLAN list for the trunk.
show trunk [mod_num/port_num]
Task
Command
Step 1
Turn off trunking on a port.
set trunk mod_num/port_num off
Step 2
Verify the trunking configuration.
show trunk [mod_num/port_num]
