Re: Policing and Tc

Thank you so much for this clarification, I am forever in the debt of most
group study users!!

This has been a great help thank you!!

On Wed, Mar 3, 2010 at 10:34 PM, Piotr Kaluzny <piotrk_at_ipexpert.com> wrote:

> Garth,
>
> You are correct.
>
> But please note two things - first, you don't set the interval but the
> CIR/Police_Rate and the Bc (first token bucket size) and optionally Be
> (second token bucket size), assuming we are talking about single-rate
> policer. Second thing is that in your example packets would get marked as
> "exceeded". They could be marked as "violated" only when violate action has
> been configure which automatically adds the second token bucket - Be.
> Violated packets are packets for which there is not enough tokens in the
> Be-bucket.
>
>
> Regards,
> --
> Piotr Kaluzny
> CCIE #25665 (Security), CCSP, CCNP
> Sr. Support Engineer - IPexpert, Inc.
> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>
>
> On Wed, Mar 3, 2010 at 2:10 PM, Garth Bryden <
> hacked.the.planet.on.28.8k.dialup_at_gmail.com> wrote:
>
>> Ok Thanks,
>>
>> So I think I am have a clear mind on how it all works now and fact is that
>> in Policing Time Intervals are completely not used to determine how many
>> tokens are in a bucket, but you can configure your bucket to be the size of
>> a certain time interval... for example 0.125ms but I believe, you must be
>> very careful doing this otherwise you would end up with more dropped packets
>> than you expected and not actually achieving the CIR that you configured.
>>
>> For example.
>>
>> If I had a CIR of 56000bps which is equal to 7000 bytes per second then I
>> should configure the bucket to be 7000 bytes at a minimum.....
>>
>> It is possible however to configure a bucket to be smaller, say I had the
>> bright idea to configure the bucket big enough for a Tc of 0.125ms
>>
>> 56000*0.125=7000bps / 8 = 875bytes
>>
>> Ok so if I configure my Token bucket for policing at 875bytes, then 1
>> second passes and I get a 1500byte packet hit the policer then policer would
>> fill up the bucket with 875 bytes worth of tokens and there would be
>> spillage of 6125 bytes worth of tokens and then the policer would see there
>> is not enough tokens in the Token Bucket and mark the packet as violating
>> then perform whatever action has been configured for violating?
>>
>> Is this correct and make sense, otherwise I'm completely screwed!
>>
>> Regards,
>>
>> Garth
>>
>>
>>
>> On Wed, Mar 3, 2010 at 5:49 PM, Piotr Kaluzny <piotrk_at_ipexpert.com>wrote:
>>
>>> Garth,
>>>
>>> Not sure if this is exactly what you want to know, but in the situation
>>> you described below packet greater than 1000B could not be transferred (or
>>> whatever action you set for exceed) assuming Be equals to 0, because the
>>> single token bucket has maximum capacity of 1000B.
>>>
>>> I would say this is more of an example for shaping. With shaping, packets
>>> are refilled every single Tc, and if Be concept is used, low activity
>>> periods can extend the total amount of time bits are serialized continuously
>>> without having to wait for the end of Tc (assuming proper Be value).
>>>
>>> In this particular example, if shaping was used, even that packet is
>>> bigger than the number of tokens (number of bits for shaping), it would be
>>> serialized in parts because shaping buffers packets. Also please note that
>>> bits are always serialized at the interface clock rate, regardless of
>>> police/shape rate.
>>>
>>> Regards,
>>> --
>>> Piotr Kaluzny
>>> CCIE #25665 (Security), CCSP, CCNP
>>> Sr. Support Engineer - IPexpert, Inc.
>>> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>>>
>>>
>>>
>>>
>>>
>>> On Wed, Mar 3, 2010 at 8:27 AM, Garth Bryden <
>>> hacked.the.planet.on.28.8k.dialup_at_gmail.com> wrote:
>>>
>>>> Thanks for the input Guys but I'm still not convinced.
>>>>
>>>> I have not been able to find any reference to this Scheduler based
>>>> approach
>>>> anywhere :|
>>>>
>>>> In my view here, I can't see any benefit here of having a token bucket
>>>> smaller than 1second of the CIR!
>>>>
>>>> This is because say for example you had a 64kbps line which equates to
>>>> 8000
>>>> bytes per second, if you configure your token bucket in an interval of
>>>> .125ms which is 1000 bytes say you had a heap of packets burst through
>>>> your
>>>> router and your token bucket is empty, then 1 second later a new
>>>> 1500byte
>>>> packet passes through the policer, wouldn't the policer then look fill
>>>> up
>>>> the token bucket, to it's maximum of 1000 bytes and consider the 1500
>>>> byte
>>>> packet to be violating (presuming a Be of 0) instead of conforming?
>>>>
>>>> Where as if the bucket could hold up to 8000 bytes it would be
>>>> considered
>>>> conforming!
>>>>
>>>> Excuse me if I am totally off track here but I am just trying to really
>>>> get
>>>> my head around it.
>>>>
>>>> Thanks heaps,
>>>>
>>>> Garth
>>>>
>>>> On Tue, Mar 2, 2010 at 2:20 PM, karim jamali <karim.jamali_at_gmail.com>
>>>> wrote:
>>>>
>>>> > Hi Garth,
>>>> >
>>>> > It seems that the either the Packet based approach or the Scheduler
>>>> based
>>>> > approach could be used (based on the minimum). We are comparing the
>>>> number
>>>> > of tokens currently in the bucke (at time t): addition of what we have
>>>> put
>>>> > CIR * (t-t1) as well as what was already in the bucket at time t1. We
>>>> > compare this value to the Bc. This comparison will lead to using
>>>> either
>>>> > packet or scheduled mode.
>>>> >
>>>> > Best Regards,
>>>> >
>>>> > Karim Jamali
>>>> >
>>>> >
>>>> > On Tue, Mar 2, 2010 at 7:06 AM, Joe Astorino <
>>>> jastorino_at_ipexpert.com>wrote:
>>>> >
>>>> >> The answer as usual is "it depends". I would have to double check but
>>>> I
>>>> >> believe it uses the lower of the two values.
>>>> >>
>>>> >> It will be the minimum of either the Bc or the interval based token
>>>> bucket
>>>> >> based on the CIR and packet arrival time
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >> Regards,
>>>> >>
>>>> >> Joe Astorino CCIE #24347 (R&S)
>>>> >> Sr. Technical Instructor - IPexpert
>>>> >> Mailto: jastorino_at_ipexpert.com
>>>> >> Telephone: +1.810.326.1444
>>>> >> Live Assistance, Please visit: www.ipexpert.com/chat
>>>> >> eFax: +1.810.454.0130
>>>> >>
>>>> >> IPexpert is a premier provider of Classroom and Self-Study Cisco CCNA
>>>> >> (R&S, Voice & Security), CCNP, CCVP, CCSP and CCIE (R&S, Voice,
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>>>> the
>>>> >> United States, Europe and Australia. Be sure to check out our online
>>>> >> communities at www.ipexpert.com/communities and our public website
>>>> at
>>>> >> www.ipexpert.com
>>>> >>
>>>> >> -----Original Message-----
>>>> >> From: Garth Bryden <hacked.the.planet.on.28.8k.dialup_at_gmail.com>
>>>> >> Date: Tue, 2 Mar 2010 11:56:00
>>>> >> To: karim jamali<karim.jamali_at_gmail.com>
>>>> >> Cc: Cisco certification<ccielab_at_groupstudy.com>
>>>> >> Subject: Re: Policing and Tc
>>>> >>
>>>> >> So what are you saying here that Policing uses a scheduler for single
>>>> rate
>>>> >> polcing but a packet based approach for dual rate policing?
>>>> >>
>>>> >> Cheers,
>>>> >>
>>>> >> Garth
>>>> >>
>>>> >> On Tue, Mar 2, 2010 at 1:20 AM, karim jamali <karim.jamali_at_gmail.com
>>>> >
>>>> >> wrote:
>>>> >>
>>>> >> > Hi Garth,
>>>> >> >
>>>> >> > This is from a previous email I sent to groupstudy and was a result
>>>> of
>>>> >> an
>>>> >> > explanation of Petr Lapukhov and Joe Astrino. I am truly thankful
>>>> to
>>>> >> both
>>>> >> > for sharing their knowledge.
>>>> >> >
>>>> >> > This is the email I sent which is sort of a summary:
>>>> >> >
>>>> >> > Dear Gents,
>>>> >> >
>>>> >> > I would like to thank Petr & Joe for such a wonderful knowledge
>>>> sharing.
>>>> >> > The main point of discussion as I understand is how the token
>>>> bucket is
>>>> >> > updated with policing:
>>>> >> >
>>>> >> > 1)Scheduler Approach which Petr mentioned relies on adding a number
>>>> of
>>>> >> > packets every scheduling interval (without having to do anything
>>>> with
>>>> >> the
>>>> >> > way packets arrive and inter-arrival time).
>>>> >> >
>>>> >> > 2)Packet based approach: which relies on the inter-arrival time of
>>>> >> packets
>>>> >> >
>>>> >> > Specifically, the token arrival rate is calculated as follows:
>>>> >> > (time between packets<which is equal to t-t1>* policer rate)/8 bits
>>>> per
>>>> >> > byte Looking at the formulas that Joe used from Cisco's website:
>>>> >> >
>>>> >> > Tc(t) = min(CIR * (t-t1) + Tc(t1), Bc)
>>>> >> > Tp(t) = min(PIR * (t-t1) + Tp(t1), Be)
>>>> >> >
>>>> >> > It seems that the either the Packet based approach or the Scheduler
>>>> >> based
>>>> >> > approach could be used (based on the minimum). We are comparing the
>>>> >> number
>>>> >> > of tokens currently in the bucke (at time t): addition of what we
>>>> have
>>>> >> put
>>>> >> > CIR * (t-t1) as well as what was already in the bucket at time t1.
>>>> We
>>>> >> > compare this value to the Bc. This comparison will lead to using
>>>> either
>>>> >> > packet or scheduled mode.
>>>> >> >
>>>> >> > Once again,Petr & Joe can't thank you enough!
>>>> >> >
>>>> >> > Best Regards,
>>>> >>
>>>> >>
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>>>> >>
>>>> >>
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>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >
>>>> >
>>>> > --
>>>> > KJ
>>>>
>>>>
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Received on Wed Mar 03 2010 - 22:37:43 ART