Policy Map, what is Conform burst?

[kutukutu9]

When creating a policy map what is the Conform burst?

In the example below what does the bc (conform burst) do? Any hard fast rules for configuring the bc?

7206#show policy-map SAN
  Policy Map SAN
    Class SAN-Class
     police cir 167772000 bc 5242875
       conform-action transmit
       exceed-action drop

I'm tyring to stop over running our 50 meg circuit to our ISP.

Many thanks for your time and efforts,

Kurt

[Wouter Prins]

Hi Kurt,

If you want to limit the traffic to your isp, it is better to setup shaping instead of policing. With policing you are dropping packets and this is what your ISP is doing inbound. So if you configure shaping outbound you are treating your traffic with care (as its being buffered) and the isp can't drop the traffic because it is conforming the contract (50Mb/s in your case).

[kutukutu9]

I have never done shaping but this sounds like a much better idea. I googled around but am not confident in the information I see. Can you provide me with a sample configuration or link so I can trust I'm getting sound information?

Thank you

[Mahesh Gohil]

Hi Kurt,

You can use shaping same as you used policing. the command is

shape average 51200000 >>> this is for 50mb bandwidth.

optionally you also can give bc and be value as per requirement.

"shape average cir bc be "...here bc value decides yor tc value. where tc=bc/cir

Note: if you have voice traffic the recommended tc value is 10ms so it get better treeatment.
and for mix type of traffic i am using bc=cir*1.5/8

so config for 50mb link will be

shape average 51200000 9600000.

And answer to your first question. what is bc

It is amount of burst allowed per tc. Meaning in above config 9600000 bits of data will be allowed in 187.5ms.

if you have bursty traffic you can increase bc value. For more information you can search cisco for "how shaping works"

Regards

Mahesh