The multi-VLAN port is a feature which allows switch for configuring a single port for two or more vlans. This feature allows users from different VLANs to access a server or router without implementing InterVLAN routing capability. A multi-VLAN port performs normal switching functions in all its assigned VLANs.

Multi-VLAN port will not work when a trunk is configured on the switch. Multi-VLAN can’t be used to connect between switches. Multi-VLAN port only used to connect a router or server. The switch automatically transitions to VTP transparent mode when the multi- VLAN port feature is enabled, making the VTP disabled.

The multi-VLAN port feature is supported only on the Catalyst 2900 XL/3500 XL series switches. This feature is not supported on the Catalyst 4000/5000/6000 series or any other Cisco Catalyst switches.

Configuration:
Switch(config-if)# switchport mode multi
To assign a multi-VLAN port already in multi mode to a range of VLANs: Switch(config-if)# switchport multi vlan 15-20