Day-29: VLAN Trunking.

By | June 12, 2022

The trunk port basically used to connect between switches. It carries traffic on one or more VLANs on the same physical links. Trunk ports are called tagged ports.

  • Can have two or more VLANs configured.
  • Can carry multiple VLAN information.
  • By default, all the VLAN traffic is allowed from a trunk port.

The trunk is basically carrying the VLAN information between the switches. And by default, all the VLANs are allowed on trunk ports.

The trunk is basically carrying the VLAN information between the switches. And by default, all the VLANs are allowed on trunk ports.

There are two trunking protocols:

  • 802.1Q: This is the most common trunking protocol. It’s a standard and supported by many vendors.
  • ISL: This is the Cisco trunking protocol. Not all switches support it.

Trunk ports mark frames with some uniquely identifying tags which are either 802.1 Q or inter-switch link (ISL) tags because they are allowed to move between the switches. They are used to add VLAN information to frames as they are transported between the switches and other devices.

Trunk & Access Ports.

basically, we use the trunk ports to carry the VLAN information between the switches. but access port is a dropping port where the frames will be forwarded as untagged VLANs.So the device will be connected to access ports that have no visibility to VLAN information.

Configuring the Trunk Ports.

Switch(config)# interface <interface>
Switch(config-if)#switchport trunk encapsulation dot1q
Switch(config-if)#switchport mode trunk
Switch(config-if)#end

Verifying VLAN and trunking

Switch# show vlan <brief>
Switch# show interface trunk
Switch#show interface status
Switch#show interface <interface> switchport

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