14 - Basic trunk & Native Vlans

Question 1

What is a trunk port ?

Answer 1

Trunk port = Allows Multiple Vlans to travel through it.

These types of ports usually connect two or more switches together.

Trunk is a Cisco term,
in other vendors Trunk is called “ Tagged” port

Question 2

What is a Native Vlan ?

What type of connection go through Native Vlan ?

What is the default No. for Native Vlan ?

Answer 2

Any Data that does not have Vlan attached to it will go through the Native Vlan.

e.g Untagged Data or connection types such as - Telnet, CDP will go through Native Vlan

Native Vlan exist by default on Vlan 1.
This can be changed

Question 3

What happens during a Native Vlan miss-match ?
Scenario below - Switch A send Data ?

Switch A - trunk is Native Vlan is numbered 20

Switch B - trunk is Native Vlan is numbered 10

Answer 3

When a device on vlan 20 from switch A, send a message through the trunk to the other side

• it should have a header with vlan 20.
• But that does not happen, why ? Because Native Vlan is for untagged data,
• It will strip the vlan20 header & replace it with a header of No vlan and then send it to the otherside.
• When switch B recives the data it will send it to vlan 10. why ? Becuase switch B Native vlan is set to 10.