sub interfaces

RUN-DMC

Could someone simply describe why and when would you implement sub interfaces on a single physical interface? thanks just trying to grasp the conecpt.

netstat

subinterfaces are a means of establishing multiple virtual links over a single physical one -which in turn makes up a virtual circuit.

The easiest way i found to explain it would be by the example of vlans. Consider a switch which is divided into 3 vlans and 3 separate switches

If u were actually using 3 switches u would need 3 cables running from each switch to a router. If instead u are using 3 vlans on the same switch, a single cable is required which runs between your router and your 3vlan-ed switch. This cable (configured and known as a TRUNK) will carry information as if it were 3 separate cables when using 3 separate switches. Therefore, for every "virtual cable" to a "virtual switch" a subinterface configuarion is required on the router.

This is just a simple example, hope this helps.

netstat

"which in turn makes up a virtual circuit."

Ignore this part cos i went into frame-relay here.. which is not true for this example! sorry