QOS| Policing single bucket

[sarahr202]

Hi everybody

I have a question on single bucket policing .

Policy-map LEE

class garbage

Police cir 56000 BC 1750

Conform action transmit

exceed action drop

int S0/0

service -policy LEE input

+++++++++++++++++++++++++

Let say a steady stream of packets belonging to class garbage arriving on s0/0

Assuming each packet is 100 bits long

In one second, we transmitted 5000 bits, so we are left with  600 tokens, next second comes  , our bucket replenishes with another 56000 bits.

In next second we transmitted 5000 bits, we are again left with 600 tokens so altogether with left excess 1200 tokens ( 600 from previous second)

1) How many maximum  excess token can we have ? Is it 1750 tokens because Bc=1750?

Scenario:2

2) Let say we have in our token bucket 56000 + 600 excess token ( from previous second)

During this one sec, first  we have received 56000 bits.  We checked our token bucket and transmitted 56000 bits, the second is not over yet,  we received 600 bitst. What will happen next? will we abe to transmit 600 bits  because we still have 600tokens left from previous sec?

++++++++++++++++++++++++++++++++++++

Scenario # 3

Let say I do not specify the conform action,, rather i just enter police 56000 and enter, What would be the default conform action if none specified as shown below:

Policy-map LEE

class garbage

Police cir 56000 BC 1750

thanks

[Joseph W. Doherty · Accepted solution]

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The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

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Posting

It appears, to me, your policer will be a "police average", which means that Be should be ignored.

If configured to "police peak" Bc and Be are used.  From some Cisco documentation, every Tc, only Bc amount of tokens should be replenished, and unused Be tokens should be carried over.  As such, Be would only be replenished with unused Bc tokens.

However, Peter did some testing on this, and found Bc and Be were both replenished each Tc, i.e. effectively policed rate was Bc + Be, for a default, effective police peak was 2x police shape.  (Personally, I think this is incorrect [not Peter's testing, but such an implementation].)

[sarahr202]

Thanks Joseph

If configured to "police peak" Bc and Be are used.  From some Cisco documentation, every Tc, only Bc amount of tokens should be replenished, and unused Be tokens should be carried over.  As such, Be would only be replenished with unused Bc tokens

1)Let say we are shaping " peak" , let say during certain tc our buffers are full, all tokens are used , we transmitted Bc bits, but our buffer are still not empy and we do not have any left over i.e exceed bucket is empty. Will we able to transmit more bits after Bc eventhough we have no tokens left  and we are shaping " peak"

2)  Just want to verify this, let say we have 100 Mbps i.e line rate is 100 Migbs, We can not  transmit faster than the line rate i.e 100 Mbs. We can not transmit at any slower than 100 Mbs. Is it correct?

thanks for your help

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

#1 Policing doesn't buffer.  What policing does is "count" bandwidth utilization during a Tc, and if its exceeded, applies the "too much" rule(s).  (A "too much" rule usually drops, but it might not drop [which seems useless, but it can be use for statistical analysis] or it might just remark [also not dropping].)

The "counting" is done by removing "tokens" for the volume of traffic seen.  When all the "tokens" are gone, then the "too much" rule(s) apply.

Peak policing provides two token buckets to draw from during the same Tc; first Bc then Be.

#2 Yes, packets are always transmitted at interface "speed".  (This also applies to shaping, the difference being unlike policing which usually drops "too much", shaping will queue/buffer packets.)