Configuration

Many modern switches do not support Cisco's ISL at all. They only support 802.1Q (dot1q).

However, switched that do support both have a trunk encapsulation of 'Auto' by default.

To manually configure the interface as a trunk port, you must first ser the encapsulation to 802.1Q or ISL. On switches that only support 802.1Q, this is not necessary.

After you set the encapsulation type, you can then configure the interface as a trunk.

Modifying Allowed VLANs

WORD

Add

Remove

All

Except

None

Changing the Native VLAN

For security purposes, it is best to change the native VLAN to an unused VLAN.

Make sure the native VLAN matches on between switches!

The show vlan brief command shows the access ports assigned to each VLAN, NOT the trunk ports that allow each VLAN.

Use the show interfaces trunk command instead to confirm trunk ports.