From: loc.pham@comcast.net
Date: Sat Dec 25 2004 - 14:10:55 GMT-3
That is true, and they give recommend values as an suggestion.
My take is on the rate -limit command values for normal & max burst rec. have also been changes, see this link:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/qos_r/qrcmdr.htm#1017761
( note that here , normal-burst = bps min/ 2000 ? he he )
If this is would happen in the lab, I am sure it would spell out somewhere or a trip to the proctor desk for what values to use.
LP.
> 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/q
> rfcmd8.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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