Eigrp metric calculation

Answered Question
Aug 11th, 2009

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.

I have this problem too.
0 votes
Correct Answer by Istvan_Rabai about 7 years 3 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 3 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

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

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

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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