Cisco IOS – Finding unused interfaces

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Have you ever looked at a comms cabinet run of Cisco switches only to find that ever interface is patched, some of them have no link lights and you don’t know which ones can be unpatched. The below steps are my method finding which interfaces have not been used in  a long time. There are plenty of tools and network monitoring solutions that could be used, the below is the native IOS method.

If you run show interface against an interface the output includes details on the last time the interface received or sent data. In the case of the below screenshot 7 weeks.

Cisco find unused ports

But if manually checking interface after interface does not sound fun then the below regex after the show interface command will return a list of all interfaces that haven’t been used in the last 6+ weeks or have never been used.

show int | i proto.*notconnect|proto.*administratively down|Last in.* [6-9]w|Last in.*[0-9][0-9]w|[0-9]y|disabled|Last input never, output never, output hang never

The command will give an output similar to the below;

Cisco find unused ports

I generally run this command and then do a show interface to check the detail and description to make sure I haven’t missed anything before un-patching the interface.

1 thought on “Cisco IOS – Finding unused interfaces”

  1. Unfortunately this command does not work 100% properly. It showed me a port which is only unused since 2 weeks.

    GigabitEthernet1/0/25 is down, line protocol is down (notconnect)
    Hardware is Gigabit Ethernet, address is 580a.20dd.8c99 (bia 580a.20dd.8c99)
    MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
    reliability 255/255, txload 1/255, rxload 1/255
    Encapsulation ARPA, loopback not set
    Keepalive set (10 sec)
    Auto-duplex, Auto-speed, media type is 10/100/1000BaseTX
    input flow-control is off, output flow-control is unsupported
    ARP type: ARPA, ARP Timeout 04:00:00
    Last input 2w0d, output 2w0d, 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
    31066381 packets input, 8796519066 bytes, 0 no buffer
    Received 620213 broadcasts (348900 multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
    0 watchdog, 348900 multicast, 0 pause input
    0 input packets with dribble condition detected
    63243708 packets output, 43477234713 bytes, 0 underruns
    0 output errors, 0 collisions, 1 interface resets
    1663 unknown protocol drops
    0 babbles, 0 late collision, 0 deferred
    0 lost carrier, 0 no carrier, 0 pause output
    0 output buffer failures, 0 output buffers swapped out

    Do you know why this happens and can this be fixed?


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