In the example, interface Fastethernet 2/1 has been configured as a trunk
link for ISL that is permanently on. DTP negotiation is not allowed. The trunk
link will carry VLAN traffic for VLANs 1-5 and 1002-1005. VLAN 2-5 are
configured on various access ports on the switch and the trunk links need to
carry the frames for these VLANs as well as the frames for the system VLANs 1,
1002-1005.
– 
 |
NOTE:
It is best practice is to shut down an interface while configuring
trunking attributes so that premature autonegotiation cannot occur.
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Configuring a Port for ISL Trunking with No DTP
When
configuring the Layer 2 trunk to not use DTP, the following syntax is used so
that the trunk mode is set to on and NO DTP messages are sent on the
interface:
- First, enter the shutdown command in the interface
mode.
- Enter the switchport trunk encapsulation command.
- Enter the switchport mode trunk command.
- Enter the switchport trunk native vlan vlan_id
command.
- Enter the switchport nonegotiate command.
- Finally, enter the no shutdown command.
This example shows how to configure a port for ISL trunking with no
DTP:
Switch#configure terminal
Enter configuration commands, one per line. End with
CNTL/Z.
Switch(config)#interface
fastethernet 2/1
Switch(config-if)#shutdown
Switch(config-if)#switchport trunk encapsulation
isl
Switch(config-if)#switchport mode
trunk
Switch(config-if)#switchport trunk native vlan
99
Switch(config-if)#switchport
nonegotiate
Switch(config-if)#no
shutdown
Switch(config-if)#end
Switch#exit
Verifying the ISL Trunk Configuration
Use
show commands to display port information, switch port
information, or trunking information.
