From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Mon Mar 22 2004 - 19:29:31 GMT-3
For those of you that don't have the workbook, the task in question is as
follows:
9.1. Network administrators in your NOC have noticed an excessive amount
of packet loss across the Frame Relay cloud between R1 and R3. After
further investigation these engineers have determined that R1 has been
overwhelming the Frame Relay connection to R3. Configure Frame Relay Traffic
Shaping on R1 in order to help resolve this issue.
9.2. R1 has a port speed of 512Kbps.
9.3. R1's DLCI 113 has a CIR of 256Kbps.
9.4. R1 should send data at 384Kbps and throttle down to CIR in the event
of congestion notification from the Frame Relay cloud.
9.5. In the case that R1 has accumulated credit, it should be allowed to
burst up to its port speed.
9.6. Use an interval (Tc) of 100ms.
The answer is:
CIR: 384000
MINCIR: 256000
Bc: 38400
Be: 12800
Adaptive shaping: BECN
The problem with the interpretation of this task is Cisco's choice
to use the phrase "CIR" when it should really say "Target Rate" or "Average
Rate".
If you talk to a telco guy, CIR is what is provisioned on the
circuit. This is technically what is (read should be) carved out as an end
to end guarantee on the circuit. In fact, many circuits actually have a CIR
of zero, meaning that nothing is guaranteed to get through.
In terms of Cisco's FRTS algorithm, CIR is simply your average
output rate. This is the rate in bits per second that packets are allowed
to leave the output queue. This does not relate at all to what is
provisioned on the circuit. This value can be configured lower, equal to,
or higher than the provisioned rate. It can even be configured higher than
what the interface is clocked at (not that it would make sense to do so).
The MINCIR value is what the router will drop down to at a minimum
in the case that a BECN is heard from the Frame Relay cloud. Typically the
MINCIR is configured to be the provisioned rate of the circuit. However,
technically these two values have no relation. The MINCIR can be configured
lower, equal to, or higher than the provisioned rate. Normally this value
*should* be the provisioned rate, as packet loss should not theoretically
occur if you are sending at or below your provisioned rate. Note that
MINCIR has no affect unless adaptive shaping is enabled.
Therefore in order to answer this question correctly you have to
make the distinction between the "telco" CIR and the "Cisco" CIR. Make
sense?
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
> alsontra@hotmail.com
> Sent: Friday, March 19, 2004 9:14 AM
> To: Ahmed Mustafa; ccielab@groupstudy.com
> Subject: Re: Internetwork Lab 5 Task 9.1 - 9.5
>
> Hi Ahmed,
>
> This task is a bit confusing, and may need to be reworded. Here's how I
> interpreted tasks 9.1-6
>
> Task 9.1 tells you that your going to be doing FTRS on R1
> Task 9.2 tells you that R1 has a Port Speed of 512k
> Task 9.3 tells you that R1 has a CIR of 256k
> Task 9.4 tells you that R1 should (meaning, change the CIR to) send data
> at
> 384k and throttle down to a CIR of 256k. <------ (This would have been
> easier to understand if they had said min CIR of 256k. This is the key
> task-
> You've just been told to use 384k as the CIR and 256k as the minCIR.
>
> Task 9.5 tells you that R1 should be allowed to burst up to port speed.
> Task 9.6 tells you that your TC=100ms
>
> Here's how I broke it down.
>
> Tc= 1000/100= 10
> CIR = 384000
> Bc = 384000/10 = 38400
> Be= (512000-384000)/10=12800
> minCIR= 256000
>
> Turn on adaptive shaping and your done. I admit that I'm making an
> assumption on the CIR and minCIR, but I think this question comes done to
> interpretation. Perhaps, I just got luck on this task! Hopefully the
> Brian's will provide us with further insight.
>
> Alsontra-
>
>
>
>
>
> ----- Original Message -----
> From: "Ahmed Mustafa" <ahmed.mustafa@sbcglobal.net>
> To: <ccielab@groupstudy.com>
> Sent: Thursday, March 18, 2004 11:14 PM
> Subject: Internetwork Lab 5 Task 9.1 - 9.5
>
>
> > Group,
> >
> > Can someone explain the following:
> >
> > Task 9.3 clearly says CIR is 256000
> > Task 9.5 states Burst up to its port speed. Bc: Wouldn't we simply use
> > 512000 for Bc instead of calculating through the formula: BC=CIR *
> Tc/1000
> >
> >
> > The solution guide states
> >
> > AR (port speed) = 512000 bps -------> agreed
> > CIR (average rate) = 384000bps -------------> if task clear says that
> CIR
> > 25600, then how to identify the correct CIR value. The task 9.4 states
> R1
> > should send data at 384000.
> >
> > Solution guide has also defined the Be eventhough is not asked to
> configured.
> >
> > Regards,
> >
> > Ahmed
> >
> > _______________________________________________________________________
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