input drops without congestion

[etamara]

Hi,
I´m running version 12.0(7)T in a Cisco 3660 with 2 FastEthernet interfaces ( let´s call them internal and external ). I see input drops growing in the external interface with rates around 10 Mbps ( config speed is 100 Full ), as shown below ( two consecutive captures ):

Router#sh int fas0/1
FastEthernet0/1 is up, line protocol is up
Hardware is AmdFE, address is 0004.c121.7aa1 (bia 0004.c121.7aa1)
Internet address is 10.12.51.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 19/255, rxload 35/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:19:25
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 2923 drops
5 minute input rate 13911000 bits/sec, 3299 packets/sec
5 minute output rate 7627000 bits/sec, 2987 packets/sec
3897766 packets input, 2141072631 bytes
Received 3832 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast
0 input packets with dribble condition detected
3500006 packets output, 1087153091 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 output buffer failures, 0 output buffers swapped out

Router#sh int fas0/1
FastEthernet0/1 is up, line protocol is up
Hardware is AmdFE, address is 0004.c121.7aa1 (bia 0004.c121.7aa1)
Internet address is 10.12.51.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 19/255, rxload 35/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:19:33
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 3035 drops
5 minute input rate 13790000 bits/sec, 3288 packets/sec
5 minute output rate 7622000 bits/sec, 2982 packets/sec
3925105 packets input, 2153365504 bytes
Received 3853 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast
0 input packets with dribble condition detected
3525661 packets output, 1096458824 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 output buffer failures, 0 output buffers swapped out

As you can see, no errors are reported.

CPU and memory doesn´t seem to be the problem:

Router#sh proc cpu
CPU utilization for five seconds: 24%/14%; one minute: 19%; five minutes: 19%

Router#sh mem sum
Head Total(b) Used(b) Free(b) Lowest(b) Largest(b)
Processor 619DF800 98699264 8577260 90122004 87693284 87762924
I/O 7800000 8388608 2552636 5835972 5595980 5815612

Switching path is Fast Switching:

Router#sh interfaces fast0/1 stats
FastEthernet0/1
Switching path Pkts In Chars In Pkts Out Chars Out
Processor 132844 17787214 13799 3057372
Route cache 4333461 2385829334 4003899 1257045194
Total 4466305 2403616548 4017700 1260102686
Router#sh interfaces fast0/0 stats
FastEthernet0/0
Switching path Pkts In Chars In Pkts Out Chars Out
Processor 18217 2364953 28431 6860030
Route cache 4034723 1266764934 4366505 2401047961
Total 4052940 1269129887 4394936 2407907991

Any guess??!??!?
Thanks,
E

 

[routerman]

Have a look at this document on cisco.com, I,ve used it whilst investigating these types of problems.

http://www.cisco.com/en/US/partner/...oducts_tech_note09186a0080094791.shtml#topic2