The status of an interface on a Cisco switch can be checked using the show interface TYPE exec mode command. Consider the following example:
SW1#show interfaces fa0/1 FastEthernet0/1 is up, line protocol is up (connected) Hardware is Lance, address is 0040.0b21.0b01 (bia 0040.0b21.0b01) BW 100000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 100Mb/s input flow-control is off, output flow-control is off ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:08, output 00:00:05, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue :0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 956 packets input, 193351 bytes, 0 no buffer Received 956 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 watchdog, 0 multicast, 0 pause input 0 input packets with dribble condition detected 2357 packets output, 263570 bytes, 0 underruns 0 output errors, 0 collisions, 10 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
As you can see from the output above, this command gives us plenty of information about the specified interface. Here is a brief description of the most important lines:
- FastEthernet0/1 is up, line protocol is up (connected) – indicates that the interface is in the up and up state
- Hardware is Lance, address is 0040.0b21.0b01 – Lance indicates the chipset used by the port. The MAC address of the port is also listed
- BW 100000 Kbit, DLY 1000 usec – the bandwidth and delay of the interface
- Full-duplex, 100Mb/s – the port operates in the full duplex mode and supports the speed of up to 100Mb/s
- 956 packets input, 193351 bytes, 0 no buffer – the total number and size of packets received by the port.
- Received 956 broadcasts – the total number of broadcast packets received by the device.
- 0 input errors, 0 CRC, 0 frame… – the number of received packets that were received incorrectly.
- 2357 packets output, 263570 bytes, 0 underruns – he total number and size of packets sent by the port.
- 0 output errors, 0 collisions – the number of packets that were not sent because of an error and the number of Ethernet collisions.