From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Wed Feb 18 2004 - 20:55:04 GMT-3
Allan,
Tc is indirectly set by configuring Bc. Tc conforms to the formula:
Tc = Bc/CIR * 1000
The maximum Tc is 125ms, and the minimum is 10ms. Incorrect
calculation will result in the default Tc being used for that CIR.
Tc is in milliseconds, Bc and Be are in bytes in CAR and in bits in
traffic-shaping. CIR/target-rate are always in bits per second.
Bc is the amount of data that must be send/received per Tc in order
to achieve the CIR/target rate over the interface. This is simply the
shaping rate over a smaller interval. The Be is the excess burst per
interval that can be sent based on previously accumulated credit.
If Bc is consistently used it is permissible that you will never be
able to burst in excess (Be).
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Allan Wells
> Sent: Wednesday, February 18, 2004 6:01 PM
> To: Brian McGahan; ccielab@groupstudy.com
> Subject: Re: Limiting ICMP using CAR
>
> Hi Brian,
>
> I have some questions relating to below TS.
>
> Getting confused : |
>
> In CAR if you set Bc to 4000 and Be to
> > 8000, it means your excess burst is actually 4000.(bytes or bits)
>
>
> Assuming TC is 1/8 =125ms CAR 128kbps
>
> rate-limit output access-group 100 128000 4000 8000 conform-action (are bc
> and be in bytes here ?)I understand tc is in bits but if bc in this
> statement is bytes that would mean TC = 250ms as 4000bytes x 8 =32000bps
> x4
> = 128kbps ?
>
>
>
> My understanding and therfor confusion is that I thought burst was only
> happening once per second not every TC in this example 125ms.Does that
> ever
> happen wherby you could only burst once per second ?
>
>
>
>
> ----- Original Message -----
> From: "Brian McGahan" <bmcgahan@internetworkexpert.com>
> To: "'Yasser Aly'" <blackyeyes00@hotmail.com>; <ccie2b@hotmail.com>;
> <ccielab@groupstudy.com>
> Sent: Thursday, February 19, 2004 1:43 AM
> Subject: RE: Limiting ICMP using CAR
>
>
> > > >So, 128,000 kbps dvided by 8 = 16,000 = bits per interval, Tc. To
> allow
> > > >for a burst of 1/4 of this rate, divide by 4. 16,000 / 4 = 4000.
> >
> > Yes and no. The interval is determined by what you configure. Your
> > target rate is 128000, which is entered in bits per second. The burst
> > committed value, which comes next, is in bytes per interval. Since it
> is
> > specified that the burst should be a quarter of the target, the rate is
> > (128000/8)/4 = 4000.
> >
> > The reason that the Be is 4000 is that there is no excess burst.
> > When Be = Bc in CAR, there is no burst. This is different from GTS and
> FRTS
> > where the configured Be is above Bc.
>
>
> >
> >
> > HTH,
> >
> > Brian McGahan, CCIE #8593
> > bmcgahan@internetworkexpert.com
> >
> > Internetwork Expert, Inc.
> > http://www.InternetworkExpert.com
> > Toll Free: 877-224-8987 x 705
> > Outside US: 775-826-4344 x 705
> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > > Yasser Aly
> > > Sent: Tuesday, February 17, 2004 7:15 PM
> > > To: ccie2b@hotmail.com; ccielab@groupstudy.com
> > > Subject: RE: Limiting ICMP using CAR
> > >
> > > Hi Packet Man,
> > >
> > > Bc and Be are configured in Bytes not bits. I am not sure about
> whether
> > > it
> > > is per Tc or not.
> > >
> > > Needs clarification.
> > >
> > > Regards,
> > > Yasser
> > >
> > > >From: "Packet Man" <ccie2b@hotmail.com>
> > > >To: blackyeyes00@hotmail.com, ccielab@groupstudy.com
> > > >Subject: RE: Limiting ICMP using CAR
> > > >Date: Tue, 17 Feb 2004 18:27:11 -0500
> > > >
> > > >Yasser,
> > > >
> > > >I think the issue you might be having is due to the different units
> used
> > > >for the different parameters. Remember that the 1st parameter, cir,
> is
> > > in
> > > >bits per SECONDS while the Bc and Be are in bits per Tc which is 1/8
> of
> > > a
> > > >second.
> > > >
> > > >So, 128,000 kbps dvided by 8 = 16,000 = bits per interval, Tc. To
> allow
> > > >for a burst of 1/4 of this rate, divide by 4. 16,000 / 4 = 4000.
> > > >
> > > >Now, given the requirements you stated, I think the answer that was
> > > >provided is wrong. I think it should be
> > > > CIR Bc
> Be
> > > >rate-limit output access-group 100 128000 16000 4000 conform-action
> > > >transmit exceed-action drop
> > > >
> > > >Hopefully, if I'm mistaken, someone will immediately say so and point
> out
> > > >my mistake. (It wouldn't be the 1st time)
> > > >
> > > >HTH
> > > >
> > > >
> > > >>From: "Yasser Aly" <blackyeyes00@hotmail.com>
> > > >>Reply-To: "Yasser Aly" <blackyeyes00@hotmail.com>
> > > >>To: ccielab@groupstudy.com
> > > >>Subject: Limiting ICMP using CAR
> > > >>Date: Tue, 17 Feb 2004 18:07:34 -0500
> > > >>
> > > >>Hi group,
> > > >>
> > > >> The task is as follows: Configure E0/0 such that ICMP traffic is
> > > limited
> > > >>to 128Kbps.
> > > >>Allow for a burst of 1/4th of this rate.
> > > >>
> > > >>
> > > >>The answer for this question was as follows:
> > > >>
> > > >>acess-group 101 permit icmp any any
> > > >>!
> > > >>interface Ethernet0/0
> > > >>rate-limit output access-group 100 128000 4000 4000 conform-action
> > > >>transmit exceed-action drop
> > > >>
> > > >>I am confused why Bc and Be were set this way. Would you kindly
> explain
> > > >>and give more detail on general concepts used when configuring Bc
> and
> Be
> > > >>while using CAR.
> > > >>
> > > >>Regards,
> > > >>Yasser
> > > >>
> > > >>_________________________________________________________________
> > > >>The new MSN 8: smart spam protection and 2 months FREE*
> > > >>http://join.msn.com/?page=features/junkmail
> > > >>http://join.msn.com/?page=dept/bcomm&pgmarket=en-
> > >
> ca&RU=http%3a%2f%2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarke
> > > t%3den-ca
> > > >>
> > >
> >>_______________________________________________________________________
> > > >>Please help support GroupStudy by purchasing your study materials
> from:
> > > >>http://shop.groupstudy.com
> > > >>
> > > >>Subscription information may be found at:
> > > >>http://www.groupstudy.com/list/CCIELab.html
> > > >
> > >
> > > _________________________________________________________________
> > > STOP MORE SPAM with the new MSN 8 and get 2 months FREE*
> > > http://join.msn.com/?page=dept/bcomm&pgmarket=en-
> > >
> ca&RU=http%3a%2f%2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarke
> > > t%3den-ca
> > >
> > >
> _______________________________________________________________________
> > > Please help support GroupStudy by purchasing your study materials
> from:
> > > http://shop.groupstudy.com
> > >
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> >
> > _______________________________________________________________________
> > Please help support GroupStudy by purchasing your study materials from:
> > http://shop.groupstudy.com
> >
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Fri Mar 05 2004 - 07:13:51 GMT-3