service policy drop rate

[talmadari]

Hi,

i have configured shaping on a interface for 37.6Mbp, while the interface NOT congested and the traffic rate is no more then 5Mbps i'm getting a drop rate and the total drops queue counter is raising.

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

      2157924144 packets, 2458512117027 bytes

      30 second offered rate 3802000 bps, drop rate 3000 bps

      Match: any

      Queueing

      queue limit 64 packets

      (queue depth/total drops/no-buffer drops) 0/41/0

      (pkts output/bytes output) 94465/86278499

      QoS Set

        dscp cs3

          Packets marked 2157806370

      shape (average) cir 37600000, bc 150400, be 150400

      target shape rate 37600000

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

      2162832613 packets, 2463933631868 bytes

      30 second offered rate 2654000 bps, drop rate 2000 bps

      Match: any

      Queueing

      queue limit 64 packets

      (queue depth/total drops/no-buffer drops) 0/4051/0

      (pkts output/bytes output) 4998926/5514847240

      QoS Set

        dscp cs3

          Packets marked 2162714137

      shape (average) cir 37600000, bc 150400, be 150400

      target shape rate 37600000

any reason for that?

why do i get packet drop in this case?

[smitesh kharecha]

Hi,

Size of you queue is 64 packets only.

Increase the queue size.

HTH,

Smitesh

[Konstantin Dunaev]

for your CIR you've choosed too small BC/BE values.

I'd suggest to increase to BC/BE value to 7050000/14100000

[Kishore Chennupati]

Hi,

Have you manually tuned the Bc and Be?. Normally its recommended to leave the values as is as Cisco would by default calculate those values. I am not saying you cant tune them but you have to be very cautious about tuning them and you need to know the exact traffic requirements

It would be good if you just use the below and not add any burst values

class class-default

   shape average 37600000

When i added this on a 7200/3630 platform I get the below  Bc and Be values

6#sh policy-map interface gigabitEthernet 1/0 output

GigabitEthernet1/0

   Service-policy output: TEST

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

      52 packets, 5168 bytes

      5 minute offered rate 0 bps, drop rate 0 bps

      Match: any

      Traffic Shaping

           Target/Average   Byte   Sustain   Excess    Interval  Increment

             Rate           Limit  bits/int  bits/int  (ms)      (bytes) 

         37600000/37600000  235000 940000    940000    25        117500 

so as u can see the Bc=94000 and Be=94000. But in your case they seem to be too low.

HTH

Kishore