Cisco CCNA Basics III- VLAN Trunk Ports

Today I am going to talk about the configuration example of VLAN trunk in the switched network. VLAN trunk port is the port which can carry more than one VLAN traffic. So, if you want to send the traffic from one access switch to another access switch having more than one VLAN traffic you need to configure that port as VLAN trunk port.

Trunk ports mark frames with unique identifying tags which can either 802.1Q tags or Interswitch Link (ISL) tags as they move between switches.

Trunk ports can be categorized into EtherChannel port groups, but all trunks in the group must have the same configuration. When a group is first created, all ports shadow the considerations set for the first port to be added to the group.

Below is the Sample topology showing the trunk ports between the switches and carry VLAN traffic. As shown in the diagram there are 3 different VLAN traffic is passed through the trunk ports.

Fig 1.1- VLAN Trunk Ports

Trunk negotiation is achieved by the Dynamic Trunking Protocol (DTP), which is a Point-to-Point Protocol (PPP). By default, a trunk port directs traffic to and accepts traffic from all VLANs. All VLAN IDs, 1 to 4094, are allowed on each trunk. However, you can remove VLANs from the allowed list, preventing traffic from those VLANs from passing over the trunk.

Basic Sample Configuration of VLAN trunk port

RouteXP-SW> enable

RouteXP-SW# configure terminal

RouteXP-SW (config)# interface Ga 1/0/1

RouteXP-SW (config-if) # switchport mode dynamic desirable

RouteXP-SW (config-if) # switchport access vlan 10

RouteXP-SW (config-if) # switchport trunk native vlan 10

RouteXP-SW (config)# interface Ga 1/0/2

RouteXP-SW (config-if) # switchport mode trunk

RouteXP-SW (config-if) # switchport trunk allowed vlan remove 20

RouteXP-SW (config)# end