Drops in WAN link

pgamage · ‎07-04-2012

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?

paolo bevilacqua · ‎07-04-2012

When working with CLI devices, please copy and past text instead of using screenshots.

pgamage · ‎07-04-2012

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#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#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 · ‎07-04-2012

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

HTH,
Niko

nkarpysh · ‎07-04-2012

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

HTH,
Niko

Joseph W. Doherty · ‎07-05-2012

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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 · ‎07-05-2012

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