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Cisco Input Queue Drops

I am getting a lot of Input Queue Drops on my serial interfaces,  does anyone have advice?
I am running ios 12.3.5b

thanks
mark anderson


CTN01-R1>sh int s0/0
Serial0/0 is up, line protocol is up
  Hardware is DSCC4 with integrated T1 CSU/DSU

  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
     reliability 255/255, txload 17/255, rxload 41/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/18265/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 249000 bits/sec, 67 packets/sec
  5 minute output rate 104000 bits/sec, 116 packets/sec
     40179782 packets input, 2024380744 bytes, 0 no buffer
     Received 82683 broadcasts, 0 runts, 0 giants, 0 throttles
     835 input errors, 123 CRC, 705 frame, 0 overrun, 0 ignored, 0 abort
     46894360 packets output, 847275657 bytes, 0 underruns
     0 output errors, 0 collisions, 13 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

CTN01-R1>sh int s0/1
Serial0/1 is up, line protocol is up
  Hardware is DSCC4 with integrated T1 CSU/DSU
 
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
     reliability 255/255, txload 19/255, rxload 36/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/16190/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 221000 bits/sec, 56 packets/sec
  5 minute output rate 118000 bits/sec, 110 packets/sec
     29346160 packets input, 3558500994 bytes, 0 no buffer
     Received 82716 broadcasts, 0 runts, 0 giants, 0 throttles
     10 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     46933834 packets output, 858223857 bytes, 0 underruns
     0 output errors, 0 collisions, 7 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up
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networkfrontier
Asked:
networkfrontier
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2 Solutions
 
anupnellipCommented:
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pseudocyberCommented:
You're getting .002% drops.  This is a lot?
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networkfrontierAuthor Commented:
I guess not,  I was not sure why I would get any.    

Do you think that increasing the input queue size would improve performance?     My CPU average is
only 20% and there is plenty of memory available.

regards
mark
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mikebernhardtCommented:
I don't think increasing your input queue would change anything. You can site for a while and hit the up arrow a bunch of times when you think the circuits are busy, and watch the queue. The output you provided shows the queues as empty at that moment.

Your output also shows CRC errors, input errors, etc. I would clear the counters and then start looking so you know that your counters are current. The input queue drops you see could have been due to problems that don't exist anymore.
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kpmasCommented:
What model of Cisco is this?  When you cleared the counters (good suggestion from mikebernhardt) did anything come back?

Seems like a lot of errors for "just" a pair of T1's...  I have a 7513 that is serving two T1's (along with 40 Megabits of other traffic on other ports) and get pretty well ZERO errors all the time....

I also don't like the number of interface resets your stats show.... this is alarming to me...

What IOS by the way?  Do you run OSPF across these lines for load balancing and/or use CEF?

Thanks,

Paul
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networkfrontierAuthor Commented:
Hi,

This is a 3620,  with IOS 12.3.5b..

We run Static routes with CEF with per-packet load sharing..  Since the clear counters we have not
seen any more interface resets.

Regards

mark
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kpmasCommented:
My best guess is possibly a carrier related issue.  We had some issues with 12.3.5b FYI but can't remember specifics right now... might want to look at 12.3.6b especially if you run snmp on that router... (security)...

Sorry, can't be of much more help unless the problem returns..

Paul
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mikebernhardtCommented:
The interface resets CRCs and input errors could easily have been related. If you had a problem with the circuit flapping (even when you were first bringing it up on this router) you would have had interface resets, which could cause the input queue drops. CRCs could also cause input drops, and they are usually due to circuit problems.

That's why I suggested clearing your counters, so you can see what's happening now. If you check them out periodically you'll have a good grip on your stats. You can also use a tool like MRTG to monitor interface stats for you, and then you can look at nice graphs.

Check out http://people.ee.ethz.ch/~oetiker/webtools/mrtg/
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