Why does "show interface" show "Last input never" when packets input is incrementing?

  • Why is it that when I perform a show interface command I see that Last input always shows never?

    FastEthernet1/31 is up, line protocol is up (connected)
      Hardware is C6k 100Mb 802.3, address is 000d.bd5a.e94e (bia 000d.bd5a.e94e)
      Description: Server
      MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
         reliability 255/255, txload 1/255, rxload 1/255
      Encapsulation ARPA, loopback not set
      Full-duplex, 100Mb/s
      input flow-control is off, output flow-control is unsupported
      ARP type: ARPA, ARP Timeout 04:00:00
      **Last input never**, output 00:03:19, output hang never
      Last clearing of "show interface" counters 1y3w
      Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
      Queueing strategy: fifo
      Output queue: 0/40 (size/max)
      5 minute input rate 2000 bits/sec, 4 packets/sec
      5 minute output rate 13000 bits/sec, 20 packets/sec
         148174387 packets input, 16331478383 bytes, 0 no buffer
         Received 465 broadcasts (0 multicast)
         0 runts, 0 giants, 0 throttles
         0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
         0 watchdog, 0 multicast, 0 pause input
         0 input packets with dribble condition detected
         798328682 packets output, 102549789248 bytes, 0 underruns
         0 output errors, 0 collisions, 0 interface resets
         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
    

    As you can see, when I run the command a couple minutes later the other counters have incremented.

    FastEthernet1/31 is up, line protocol is up (connected)
      Last input never, output 00:01:39, output hang never
      5 minute input rate 2000 bits/sec, 4 packets/sec
      5 minute output rate 14000 bits/sec, 20 packets/sec
         148176042 packets input, 16331609502 bytes, 0 no buffer
         798337129 packets output, 102550523914 bytes, 0 underruns
    

    What platform is this on, and is this a routed port?

  • Aaron

    Aaron Correct answer

    9 years ago

    There are several interface counters that don't work as well as they used to. Sometimes this is because the chassis/router has a 'fast' switching mode (CEF, or something else), and that particular 'bucket' never gets hit. Another reason might be that that particular counter only works in L3 mode instead of L2 mode. This kind of stuff is quite common, unfortunately on cisco products, particularly on the 6500 which has an enormous amount of legacy code/architecture weighing it down.

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Content dated before 7/24/2021 11:53 AM