In the example, under the show interfaces FastEthernet0/1 command, look at a line that shows something such as: Last input 00:00:41, output 00:00:00, output hang never.This shows the last time a port sent or received traffic. Likewise, the Last input never, output never, output hang never status means the port is not in use.
This is an example of output from the show interfaces command for an interface:
Switch#show interfaces FastEthernet0/1 FastEthernet0/1 is up, line protocol is up Hardware is Fast Ethernet, address is xx.xx.xx.xx
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive not set Auto-duplex (Full), Auto Speed (100), 100BaseTX/FX ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:41, output 00:00:00, output hang never !--- This line shows the uptime or downtime status.