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troubleshooting high number of collisions on cisco 3640

Posted on 2002-07-12
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Last Modified: 2008-03-06
I'm noticing a high number of collisions and deferred packets on my ETH connection Nothing has changed on my network. I have about 30 boxes connected to my 3640. One guy is saying that his downloads are very slow but
his uploads are fast. This seems odd but it got me looking at the router.

 What should I be looking for. Does this asymetric complaint seem legitimate.


Hardware is AmdP2, address is 0010.7b5a.8141 (bia 0010.7b5a.8141)
  Internet address is 63.237.136.1/24
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 22/255
  Encapsulation ARPA, loopback not set, keepalive set (10 sec)
  ARP type: ARPA, ARP Timeout 00:06:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 00:03:14
  Queueing strategy: fifo
  Output queue 0/40, 0 drops; input queue 0/75, 0 drops
  5 minute input rate 830000 bits/sec, 237 packets/sec
  5 minute output rate 896000 bits/sec, 224 packets/sec
     42825 packets input, 16824308 bytes, 0 no buffer
     Received 284 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 input packets with dribble condition detected
     42083 packets output, 20129824 bytes, 0 underruns
     0 output errors, 2408 collisions, 0 interface resets
                                ^^^^^^^^^^^^^^^
     0 babbles, 0 late collision, 1425 deferred
                                                    ^^^^^^^^^^^^^
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

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Question by:duficy
11 Comments
 
LVL 79

Expert Comment

by:lrmoore
ID: 7150313
The errors counts are and dropped packets count for much more than collisions. There are zero of both here.
The collisions indicates that the router is plugged into a hub rather than a switch. Switches stop collisions.

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Expert Comment

by:lrmoore
ID: 7150325
As far as the slow downloads go, do you have any access-lists / filters, or a firewall in the mix?
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Author Comment

by:duficy
ID: 7150360
the router is plugged into a switch
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Expert Comment

by:lrmoore
ID: 7150385
If it is plugged into a switch, then there should never be any collisions. Try a different switch port, make sure there is no speed/duplex mismatch, and try a new patch cable.
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Author Comment

by:duficy
ID: 7150401
how do I display/change duplex settings
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Expert Comment

by:edmonds_robert
ID: 7150435
From interface configuration mode:
speed 100 (or speed 10)
duplex auto|full|half
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Expert Comment

by:lrmoore
ID: 7150445
Depends on the switch...
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Expert Comment

by:lrmoore
ID: 7150449
It should be set to 10/half because your 3640 only has a 10Mb port:
MTU 1500 bytes, BW 10000 Kbit,
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Author Comment

by:duficy
ID: 7154727
SORRY I WAS GIVEN THE WRONG INFO.

It turns out it's a 2500 router. We plugged the router into a 10 megabyte hub and a laptop into the hub. We tried different ports and different cables. Still getting SLOW downloads but FAST uploads.


Ethernet0 is up, line protocol is up
  Hardware is Lance, address is 0000.0c3f.2937 (bia 0000.0c3f.2937)
  Internet address is 209.113.196.1/24
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255
  Encapsulation ARPA, loopback not set, keepalive set (10 sec)
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:22, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Queueing strategy: fifo
  Output queue 0/40, 0 drops; input queue 0/75, 0 drops
  5 minute input rate 32000 bits/sec, 2 packets/sec
  5 minute output rate 27000 bits/sec, 3 packets/sec
     3452 packets input, 2678973 bytes, 0 no buffer
     Received 21 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 input packets with dribble condition detected
     3437 packets output, 2663292 bytes, 0 underruns
     0 output errors, 9 collisions, 5 interface resets
     0 babbles, 0 late collision, 17 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out
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Accepted Solution

by:
scraig84 earned 150 total points
ID: 7157299
Lrmoore - I am a bit surprised by some of your posts -

"The collisions indicates that the router is plugged into a hub rather than a switch. Switches stop collisions."

and

"If it is plugged into a switch, then there should never be any collisions. Try a different switch port, make sure there is no speed/duplex mismatch, and try a new patch cable."

A switch port does not "stop collisions", but it is the barrier of a collision domain.  Even with a single device plugged into a switch port, if both are set to half-duplex such as in this case (and you have no option to do otherwise with that hardware), than collisions can and will happen.  Therefore, collisions are not indicitive that a hub is present, but instead indicates that either half-duplex communications are present and normal operation is occuring, or a duplex-mismatch is present.

duficy - What you are seeing looks pretty normal.  I think you may want to focus your attention on something other than the router.
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Author Comment

by:duficy
ID: 7157618
Thanks, I will look elsewhere. I suspect the problem could be the line.
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