VLAN Trunk Cisco IOS

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Configuring a trunk port

Cisco materials

VLAN trunks

A VLAN trunk is a connection between two switches where traffic from one or more VLAN's are transmitted between switches.

Trunk between two switches carrying traffic from VLAN 100 and VLAN 200 between the Switches

Configuring Trunk ports

Basic Cisco 2950 and 2960 switch configuration

Cisco 2950 and 2960 switch series only supports the 802.1Q - DOT1Q - trunk protocol.

SW2(config)#interface gigabitEthernet 0/1
SW2(config-if)#switchport mode trunk

Basic Cisco 3550 and 3560 switch configuration

Cisco 3550 and 3560 switch series supports the 802.1Q - DOT1Q - and Cisco ISL trunk protocols.

CoreSW1(config)#int fastEthernet 0/24
CoreSW1(config-if)#switchport trunk encapsulation dot1q
CoreSW1(config-if)#switchport mode trunk

IEEE 802.1Q trunk protocol

The IEEE 802.1Q is a trunk protocol defined by IEEE. See the related articles.

Defining native VLAN

Default native VLAN in the IEEE 802.1Q protocol is VLAN 1. The native VLAN is the only untagged VLAN in a trunk. Because off security you would change the native vlan. Remember: The native VLAN should be changed to the same VLAN in all Switches in the Switchblock.

Switch1(config)#<input>int fa0/3</input>
Switch1(config-if)#<input>switchport trunk native vlan 7</input>