Re: Policing and dropping packets

If you are talking about shaping that would be accurate but we are not. If
you are talking about policing, that is not accurate.

 With shaping, the bucket refill rate is based on a static amount of time,
Tc (you get Bc tokens every Tc time interval) and the shaped rate. With
policing the bucket refill rate is not based on a set static amount of
time. It is based on the interval of time between packets and the policed
rate per the formula (T-T1) * policer rate)/8 bytes. T1 would be the
current time when the packet is arriving and T would be the time the last
packet arrived. Essentially, the policer is pro-rating the amount of tokens
that get put into the bucket when the packet arrives. With policing, BC and
BE are literally a fixed size of bytes which is why you specify a fixed size
and not a rate at the command line when configuring it

See
http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_n1.html#wp1060117and/or
read up on single rate three color policers

On Thu, Jul 21, 2011 at 12:47 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> Hmm,
> Be/Bc/Tc are ways to describe a rate measure. There is no buffer involved,
> in the sense of a memory chunk, AFAIK.
>
> -Carlos
>
>
> Joe Astorino @ 21/7/2011 13:20 -0300 dixit:
>
>> Let me be a little bit more precise -- The BE bucket is just a bunch of
>> bytes. So, when you configure the BE to be 8000 bytes you are literally
>> defining the size of that bucket. Now, as you go along you may see anywhere
>> from 0 - 8000 bytes in the bucket, but the SIZE of the bucket never changes.
>> You can NEVER have more than 8000 bytes in the bucket, as overflow of the
>> BE is just spilled out and lost
>>
>> On Thu, Jul 21, 2011 at 12:17 PM, Joe Astorino <joeastorino1982_at_gmail.com<mailto:
>> joeastorino1982_at_gmail.**com <joeastorino1982_at_gmail.com>>> wrote:
>>
>> Pretty close. The BE bucket won't ever exceed 64,000 bits though
>> because you defined it to be a size of 64,000 bits -- no more, no
>> less. That doesn't change. If a packet comes in, and the BC bucket
>> is EMPTY (no tokens left -- you've used them all) and the BE bucket
>> is EMPTY (no tokens left because you used them all) it will drop the
>> packet
>>
>>
>> --
>> Regards,
>>
>> Joe Astorino
>> CCIE #24347
>> Blog: http://astorinonetworks.com
>>
>> "He not busy being born is busy dying" - Dylan
>>
>>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net