Interface status codes

Interface status codes can tell you whether an interface on a Cisco router or a switch is working. Status codes of an interface can be displayed using the show interface TYPE command, e.g.:

SW1#show interface fa0/1
FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Lance, address is 0060.70d8.0001 (bia 0060.70d8.0001)
 BW 100000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)

The first line of the output indicates the working state of the interface. The first status code (known as line status) indicates that the Layer 1 is working (FastEthernet0/1 is up). The second status code (known as protocol status) indicates that Layer 2 is also working (line protocol is up) and is always Down if the line status is Down. Finally, the word at the end of the line indicates the working state of the interface (connected in our case).

All possible combinations of the status codes are given in the table below:

Cisco interface status codes

NOTE
Only interfaces with status codes of up and up will forward or receive frames.