Eigrp metric calculation

Answered Question
Aug 11th, 2009
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Hi every body.


According to my book, eigrp uses following formula for metric calculation by default( only bandwidth and delay).

m= { (10 exp 7/bandwidth) *delay}*256


Let say router receives two updates about a network 10.0.0.0.

First update list delay 200 micro seconds

minimum bandwidth along the path 10G


Second update

delay 200 u sec

miminmum bandwidth 1G


router takes first updates then calculates the delay 10 micro seconds unit 1.e 200/10= 20

router then find the reported bandwidth is less than the one configured on the int, the update was received.


Router use theabove fomula plugging the values as:


M ={(10exp 7/10 exp 9)*20}*256


According to my book, the ( 10exp 7/10 exp 9) will be rounded down to closer interger. With this mind , would the router calculate and find the same metric value for two updates ?




Thanks a lot.

Correct Answer by Istvan_Rabai about 7 years 10 months ago

Hi Sarah,


The formula is:

metric = (10exp7/Bandwidth + SumofDelays/10)*256


Where Bandwidth is in kbps, SumofDelays is in microseconds and is the total delay along the path.


According to your data:

1st update:

(10exp7/10000000 (kbps) + 200/10)*256 = 5376


2nd update:

(10exp7/1000000 (kbps) + 200/10)*256 = 7680


The integer is calculated when the 10exp7/bandwidth calculation is done.


For example:

bandwidth=512 kbps

delay 200 microseconds


(10exp7/512(kbps) + 200/10) = (19531 + 20)*256 = 5005056.


Cheers:

Istvan

Correct Answer by Lucien Avramov about 7 years 10 months ago

The router also rounds to the closer integer, it should be the same value.

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Correct Answer
Lucien Avramov Tue, 08/11/2009 - 09:10
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The router also rounds to the closer integer, it should be the same value.

Correct Answer
Istvan_Rabai Tue, 08/11/2009 - 09:23
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Hi Sarah,


The formula is:

metric = (10exp7/Bandwidth + SumofDelays/10)*256


Where Bandwidth is in kbps, SumofDelays is in microseconds and is the total delay along the path.


According to your data:

1st update:

(10exp7/10000000 (kbps) + 200/10)*256 = 5376


2nd update:

(10exp7/1000000 (kbps) + 200/10)*256 = 7680


The integer is calculated when the 10exp7/bandwidth calculation is done.


For example:

bandwidth=512 kbps

delay 200 microseconds


(10exp7/512(kbps) + 200/10) = (19531 + 20)*256 = 5005056.


Cheers:

Istvan

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