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Drops in WAN link

Unanswered Question
Jul 4th, 2012
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Hi,


We have 512 link and observe output drops and application timeouts. Link utilization is not very high.


When ping with 1500 bytes, it shows output drops and when ping with default packet size, no output drops observed.


Service policy also in effect and shows some drops.


I have attached the screen captuers.


Is there anything wrong with serial link?

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paolo bevilacqua Wed, 07/04/2012 - 16:40
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When working with CLI devices, please copy and past text instead of using screenshots.

pgamage Wed, 07/04/2012 - 18:24
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Here is the command out puts


R1#sh int serial 3/2:0 | in rate

  Queueing strategy: weighted fair

  30 second input rate 177000 bits/sec, 223 packets/sec

  30 second output rate 208000 bits/sec, 226 packets/sec

R1#

R1#sh int serial 3/2:0 | in drops

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 95

  Output queue: 0/2000/64/0 (size/max total/threshold/drops)

R1#

R1#

R1#

R1#ping 1.1.1.1 rep

R1#ping 1.1.1.1 repeat 200


Type escape sequence to abort.

Sending 200, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Success rate is 100 percent (200/200), round-trip min/avg/max = 4/5/8 ms



R1#sh int serial 3/2:0 | in drops

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 98

  Output queue: 0/2000/64/0 (size/max total/threshold/drops)

R1#



R1#ping 1.1.1.1 repeat 200 si 1500


Type escape sequence to abort.

Sending 200, 1500-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!..!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!.!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Success rate is 97 percent (194/200), round-trip min/avg/max = 24/27/64 ms

R1#



R1#

R1#sh int serial 3/2:0 | in drops

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 120

  Output queue: 0/2000/64/0 (size/max total/threshold/drops)

R1#



R1#sh pol

R1#sh policy-map in

R1#sh policy-map interface ser 3/2:0

Serial3/2:0


  Service-policy input: ABC


    Class-map: class-default (match-any)

      33346 packets, 4157374 bytes

      30 second offered rate 197000 bps, drop rate 0 bps

      Match: any

        33346 packets, 4157374 bytes

        30 second rate 197000 bps

      police:

          cir 512000 bps, bc 64000 bytes, be 128000 bytes

        conformed 33298 packets, 4017708 bytes; actions:

          transmit

        exceeded 113 packets, 131400 bytes; actions:

          drop

        violated 14 packets, 13444 bytes; actions:

          drop

        conformed 194000 bps, exceed 0 bps, violate 0 bps


  Service-policy output: ABC


    Class-map: class-default (match-any)

      33822 packets, 4114448 bytes

      30 second offered rate 196000 bps, drop rate 0 bps

      Match: any

        33822 packets, 4114448 bytes

        30 second rate 196000 bps

      police:

          cir 512000 bps, bc 64000 bytes, be 128000 bytes

        conformed 33651 packets, 3956556 bytes; actions:

          transmit

       exceeded 154 packets, 154472 bytes; actions:

          drop

        violated 3 packets, 3084 bytes; actions:

          drop

        conformed 191000 bps, exceed 0 bps, violate 0 bps

R1#

nkarpysh Wed, 07/04/2012 - 19:07
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Hello,


Why you just don't believe that it is your policing working? It is doing what it is supposed to do - drop traffic above CIR. You may want to chenge your policing config if you want to allow more traffic to pass through.


Nik

nkarpysh Wed, 07/04/2012 - 19:08
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Just to add to the coment above. Interface utilization can be low in average but can have short bursts of traffic. Those cause policing to drop the overhead.


Nik

Joseph W. Doherty Thu, 07/05/2012 - 10:18
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Posting


Nik has likely touched upon the most likely issue, i.e. low average utilization can have have short traffic bursts.


Look at your original post's policy.GIF.  The second interfaces shows low average offered rate, but the policer is dropping some packets.


More likely than there being something wrong with you serial link, your policing policy might be suboptimal.

Alessio Andreoli Thu, 07/05/2012 - 10:26
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perform an extended ping changing dynamically the size of the packet you send out.


It maybe be useful to understand the max MTU you are at the moment able to transmit.



Alessio

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