Configuring an ISL Trunk
Step 1. Configure an ISL trunk
set trunk mod_num/port_num [on | desirable | auto | nonegotiate] isl
Step 2. Verify the trunking configuration.
show trunk [mod_num/port_num]
例：
Console (enable) set trunk 1/1 on
Port(s) 1/1 trunk mode set to on.
Console (enable) 06/16/1998,22:16:39TP-5:Port 1/1 has become isl trunk
06/16/1998,22:16:40:PAGP-5:Port 1/1 left bridge port 1/1.
06/16/1998,22:16:40:PAGP-5:Port 1/1 joined bridge port 1/1.
Console (enable) show trunk
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 on isl trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/1 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/1 1,521-524
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/1
This example shows how to place a port in desirable mode and how to verify the trunk configuration. This example assumes that the neighbor port is in auto mode.
Console (enable) set trunk 1/2 desirable
Port(s) 1/2 trunk mode set to desirable.
Console (enable) 06/16/1998,22:20:16TP-5:Port 1/2 has become isl trunk
06/16/1998,22:20:16:PAGP-5:Port 1/2 left bridge port 1/2.
06/16/1998,22:20:16:PAGP-5:Port 1/2 joined bridge port 1/2.
Console (enable) show trunk 1/2
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/2 desirable isl trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/2 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/2 1,521-524
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/2
Console (enable)
Configuring an IEEE 802.1Q Trunk
Step 1. Configure an 802.1Q trunk.
set trunk mod_num/port_num [on | desirable | auto | nonegotiate] dot1q
Step 2. Verify the trunking configuration.
show trunk [mod_num/port_num]
This example shows how to configure an IEEE 802.1Q trunk and how to verify the trunk configuration in software release 4.2 and later:
Console (enable) set trunk 2/9 desirable dot1q
Port(s) 2/9 trunk mode set to desirable.
Port(s) 2/9 trunk type set to dot1q.
Console (enable) 07/02/1998,18:22:25TP-5:Port 2/9 has become dot1q trunk
Console (enable) show trunk
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
2/9 desirable dot1q trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
2/9 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
2/9 1,5,10-32,101-120,150,200,250,300,400,500,600,700,800,900,1000
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
2/9 5,10-32,101-120,150,200,250,300,400,500,600,700,800,900,1000
Console (enable)
This example shows how to configure an IEEE 802.1Q trunk in software release 4.1:
Console (enable) set trunk 4/5 nonegotiate dot1q
Port(s) 4/5 trunk mode set to nonegotiate.
Port(s) 4/5 trunk type set to dot1q.
Console (enable) 2/20/1998,23:38:35ISL-5:Port 1/1 has become dot1q trunk
Defining the Allowed VLANs on a Trunk
Step 1. Remove VLANs from the allowed VLANs list for a trunk.
clear trunk mod_num/port_num vlans
Step 2. (Optional) Add specific VLANs to the allowed VLANs list for a trunk.
set trunk mod_num/port_num vlans
Step 3. Verify the allowed VLAN list for the trunk.
show trunk [mod_num/port_num]
This example shows how to define the allowed VLANs list for trunk port 1/1 to allow VLANs 1-100, VLAN 250, and VLANs 500-1005, and how to verify the allowed VLAN list for the trunk:
Console (enable) clear trunk 1/1 101-499
Removing Vlan(s) 101-499 from allowed list.
Port 1/1 allowed vlans modified to 1-100,500-1005.
Console (enable) set trunk 1/1 250
Adding vlans 250 to allowed list.
Port(s) 1/1 allowed vlans modified to 1-100,250,500-1005.
Console (enable) show trunk 1/1
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 desirable isl trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/1 1-100,250,500-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/1 1,521-524
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/1 1,521-524
Console (enable)
Disabling a Trunk Port
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]
-------------------------------------------------------------------------
Step 1. Return the port to the default trunking type and mode for that port type.
clear trunk mod_num/port_num
Step 2. Verify the trunking configuration.
show trunk
ISL Trunk Configuration Example
Step 1 Enter the set trunk command to configure port 1/1 on Switch 1 as an ISL trunk port. By specifying the desirable keyword, the trunk is automatically negotiated with the neighboring port (port 1/2 on Switch 2). ISL encapsulation is assumed based on the hardware type.
Switch1 (enable) set trunk 1/1 desirable
Port(s) 1/1 trunk mode set to desirable.
Switch1 (enable) 06/18/1998,12:20:23TP-5:Port 1/1 has become isl trunk
06/18/1998,12:20:23:PAGP-5:Port 1/1 left bridge port 1/1.
06/18/1998,12:20:23:PAGP-5:Port 1/1 joined bridge port 1/1.
Switch1 (enable)
Step 2 Enter the show trunk command to check the configuration. The Status field in the screen output indicates that port 1/1 is trunking.
Switch1 (enable) show trunk 1/1
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 desirable isl trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/1 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/1 1,521-524
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------