From: mani poopal (mani_ccie@yahoo.com)
Date: Sat Dec 25 2004 - 01:28:25 GMT-3
Hi Guys,
In the examples given on the link the recommended values for extended burst is 2xnormal burst. But in the examples, the values for extended burst is not 2x the normal burst. What do you guys think
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_r/qrfcmd8.htm#1037428
Policing Traffic with CAR
CAR embodies a rate-limiting feature for policing traffic. When policing traffic with CAR, Cisco recommends the following values for the normal and extended burst parameters:
normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
extended burst = 2 * normal burst
With the listed choices for parameters, extensive test results have shown CAR to achieve the configured rate. If the burst values are too low, then the achieved rate is often much lower than the configured rate.
For more information about using CAR to police traffic, see the "Policing with CAR" section of the "Policing and Shaping Overview" in the Cisco IOS Quality of Service Configuration Guide, Release 12.2.
Examples
In the following example, the rate is limited by application:
All World Wide Web traffic is sent. However, the MPLS experimental field for web traffic that conforms to the first rate policy is set to 5. For nonconforming traffic, the IP precedence is set to 0 (best effort). See the following commands in the example:
rate-limit input rate-limit access-group 101 20000000 24000 32000 conform-action
set-mpls-exp-transmit 5 exceed-action set-mpls-exp-transmit 0
access-list 101 permit tcp any any eq www
FTP traffic is sent with an MPLS experimental field of 5 if it conforms to the second rate policy. If the FTP traffic exceeds the rate policy, it is dropped. See the following commands in the example:
rate-limit input access-group 102 10000000 24000 32000
conform-action set-mpls-exp-transmit 5 exceed-action drop
access-list 102 permit tcp any any eq ftp
Any remaining traffic is limited to 8 Mbps, with a normal burst size of 16,000 bytes and an excess burst size of 24000 bytes. Traffic that conforms is sent with an MPLS experimental field of 5. Traffic that does not conform is dropped. See the following command in the example:
rate-limit input 8000000 16000 24000 conform-action set-mpls-exp-transmit 5
exceed-action drop
thanks
Mani
==============================================
loc.pham@comcast.net wrote:Mani, IMO, the author using the 128k line as a ref. bandwidth, and that is why.
GS have lot of disc. of howto, here is one link:
http://www.groupstudy.com/archives/ccielab/200303/msg01827.html
HTH,
Have a happy holiday,
LP
> Hi Tim,
>
> Thanks for getting back to me. Look at the example form cisco press lab
practise
> guide(lab5 QOS), In the example average is given as 20mbps.
>
> I would calculate bc as follows:
>
> 20 mbps=20,000,000bps
>
> 20000000*(1/8)=2500000bits (tc is assumed as defualt 1/8sec or 125ms)
> 2500000/8=312500bytes(bits to byte conversion)
>
> EXAMPLE GIVEN IN THE DEBRIEF SECTION::
> rate-limit output access-group 101 20000000 24000 32000 conform-action
> set-prec-transmit 5 exceed-action set-prec-transmit 0
>
> So if it is either MQC police command or rate-limit command I would use 312500
> for both bc and be. But the example uses:24000 and 32000 bytes. I am not
sure
> how the author came up with 24000 byts and 32000 bytes for normal and extended
> burst values. I think we have to get it right because even in the exam we
have
> to type right numbers.
>
> Mani
>
>
>
>
> ccie2be wrote:
> Mani,
>
> Off-hand, I don't know the answer to your question but here are a couple
> thoughts:
>
> 1) Given that's there's nothing that can be done using the rate-limit
> command that can NOT be done
>
> using the police MQC, and Cisco's direction is to do all QoS with MQC, I
> would doubt that you would
>
> ever need to use the rate-limit command in the lab.
>
> 2) Does the command (either rate-limit or police) require that a value for
> Bc is entered? I'm not sure, but I think
>
> it's possible that you don't need to enter a Bc value and therefore, you can
> let IOS compute that value.
>
> 3) If the Bc must be entered, just use the same value but converted to
> bytes.
>
> HTH, Tim
>
> ----- Original Message -----
> From: "mani poopal"
> To:
> Sent: Friday, December 24, 2004 8:07 AM
> Subject: QOS- CAR rate-limit statement's normal/extended burst
>
>
> > Hi Guys,
> >
> > In the rate limit statement or question if only rate is given(assue
> 20mbps), how do we arrive at values for extended and normal burst sizes. I
> know this has been discussed earlier but any help is appreciated.
> > eg:
> > rate-limit output access-group 101 20000000 24000 32000 conform-action
> set-prec-
> > transmit 5 exceed-action set-prec-transmit 0
> >
> > ps:
> > 20000000- in bits per second
> > 24000----bytes
> > 32000----bytes
> > How do they arrive at 24000 and 32000 values.
> >
> > thanks
> >
> > Mani
> >
> >
> >
> > B.ENG,A+,CCNA,CCNP,CCNP-VOICE, CSS1,CNA,MCSE
> > (416)431 9929
> > MANI_CCIE@YAHOO.COM
> >
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>
>
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