I have observed that on almost all of our Layer 2, fastEthernet ports, on the Catalyst 6500 /w SUP720, the input queue drop is always increasing, albeit slowly.
FastEthernet2/1 is up, line protocol is up (connected)
Hardware is C6k 100Mb 802.3, address is 000b.466b.a608 (bia 000b.466b.a608)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:29, output 00:00:37, output hang never
Last clearing of "show interface" counters 00:51:20
Input queue: 0/2000/308/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 6000 bits/sec, 1 packets/sec
5 minute output rate 31000 bits/sec, 24 packets/sec
9791 packets input, 2472760 bytes, 0 no buffer
Received 742 broadcasts (505 multicasts)
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
78242 packets output, 11831951 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
I have tried to search the internet for an explanation of this but can find very little information. It has been suggested that it could be caused by Layer 2 control frames that are being punted to the CPU and then dropped, such as DTP, or BPDU messages.
Can anyone shed any light on this ?
Incidentally, all links are very low utilisation, with no layer 1 / layer faults.