Calculate delay in EIGRP

mahmoodmkl · ‎05-13-2007

Hi

Guy's can anyone point me how do we calculate the dealy for eigrp metric,i m a bit confused.i know that eigrp metric is bandwidth+dealy is this delay of the interface or ...?

Thanks

Mahmood

Jon Marshall · ‎05-13-2007

Hi Mahmood

From EIGRP paper

=============================================

EIGRP uses the following formula to scale the delay:

delay = delay(i) * 256

where delay(i) is the sum of the delays configured on the interfaces, on the route to the destination network, in tens of microseconds. The delay as shown in the show ip eigrp topology or show interface commands is in microseconds, so you must divide by 10 before you use it in this formula. Throughout this paper, we use delay as it is configured and shown on the interface.

=============================================

Delay is a static value ie it doesn't change dynamically.

If you do a "sh interface" delay is displayed in microseconds. You can change the delay of the interface to affect routing choices by EIGRP and this is considering teh most reliable way to affect metrics as opposed to changing the bandwidth which has knock on effects to things such as QOS.

All interfaces from the source to the destination have their delays included in the EIGRP metric calculation.

Hope this has answered your question.

Jon

mahmoodmkl · ‎05-14-2007

Hi Jon thanks for the reply.

As it says that the delay will be in tens of microseconds but the delay under interface is in microseconds,so how get the delay from the microseconds to tens of microseconds,sorry my math is poor.

Thanks

Mahmood

Jon Marshall · ‎05-14-2007

Hi Mahmood

My maths isn't that great either :-) but i believe you just need to divide the figure shown under the interface command by 10 to get the delay.

HTH

Jon

ankbhasi · ‎05-14-2007

Hi Mahmood,

I will try to keep it very simple. To calculate EIGRP metrics in general we take delay and bandwidth which is configured on the interface assuming all K values are set to default.

To calculate EIGRP metric the formula is

[(10 to the power 7/min bandwidth) + (total delay)] * 256

Now which value of delay you will consider is your question correct?

The delay as shown in the show ip eigrp topology or "show interface" commands is in microseconds, so you must divide by 10 before you use it in this formula.

HTH

Ankur

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Mohamed Sobair · ‎05-14-2007

Hi Mahmoud,

In addition To jon's post, I am attaching here a file that will help you viewing how metric is calculated in a routing protocols such as (Eigrp & IGRP).

Regards,

Mohamed

ronbuchalski · ‎01-20-2009

The information provided is very valuable. However, it looks like the original poster has the same question that I have (and found this thread while searching for the answer):

The question is: How does IOS calculate the default value of delay for an interface? This is what I've collected:

INTERFACE BW (Kbit) DELAY (usec)

GigE 1000000 10 usec

FastE 100000 100 usec

Ethernet 10000 1000 usec

Serial (up to 2M) 2000 20000 usec

ATM DS3 40704 190 usec

ATM OC3 149760 80 usec

Also, when changing the BW from the default value to the specific value for a given circuit, I believe the Delay should be changed as well to reflect the real Delay. But again, how is it calculated?

Thank you,

Ron Buchalski