[FRED]

Hi,

What is the purpose of configuring a switch port as a trunk port?

[Jay Whale]

Hi,

What is the purpose of configuring a switch port as a trunk port?

@FRED,
A trunk port is a port that has been configured to allow multiple VLAN's to pass over it. By default a switch only allows traffic to flow from the same VLAN to the same VLAN. So if I have a 24 port switch and 12 ports are configure to be in VLAN 10 and the other 12 ports are configured to be in VLAN 20, traffic from VLAN 20 can only be sent on ports that are in VLAN 20 and the same will apply to VLAN 10. The problem with this type of solution is that how can traffic go from one switch to another switch (or switch to router)? In my example above, it would mean that I need 2 separate cables to join two switches together, 1 cable to allow traffic from VLAN 10 and a separate cable for VLAN 20. Not the end of the world if I only have 2 VLANS but if I have 20 or 50 VLANS it becomes impossible and this is where a trunk port needs to be configured. The trunk port will allow traffic from any VLAN (by default, but you can restrict VLANS on a trunk) to pass over a single port and cable. This allows us to send traffic from multiple VLAN's from one switch to another switch, or from one switch to a router.