Question

What layer of the Internet protocol does a non-routing switch operate at? What values does it use to determine output port? If it does not hold this value in its table, what is its default action?

Answer 1

A non - routing switch operate at Layer 2 (Data Link Layer) of the internet protocol.

It uses MAC address to determine output port. Each packet which comes to switch contains source and destination physical address in it, on basis of which switch forwards packet to other machine. Switch always sent packet based on destination MAC address. If MAC Address is found, packet is sent out to port against which MAC Address was matched.

For this switch uses one table in its cache memory called MAC Address table or Forwarding Table in which switch stores that at which port which machine is connected by storing its physical address (MAC Address). So table contains two columns (Physical Address and Port Number) and rows equal to number of ports in switch. When switch is turned ON, by default there is no entry in MAC address table, as communication starts, based on devices involved entries are created in table.

If MAC address not found then ARP Request is generated and MAC address is obtained. If MAC Address not found then the packet is broadcasted to all ports, except on which it has received the packet.