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Purple

## EIGRp cost calculation

I have been having this doubt of EIGRP cost formula...after reading 5 different books describing in different formats.

Cost = 256*( [ k1*BWmin + (K2* BWmin) / (256-LOAD) + K3* DELAYsum] * X )

BW = 10 exp 7 / bandwidth of slowest link

X = k5 / (reliability + k4)

and also by default k1 = k3 = 1

k2 = k4= k5 = 0

If k5 = 0...the cost becomes 0....

so if k1 and k3 are the only factors that is = 1 shouldnt the value of X =1 so that...

Cost = 256 * (BW + Delay)

I hope i am clear.

One more question is....the formulae for bandwidth...

is it 10 exp 7 or 10 exp 8

Shanky

2 REPLIES
Cisco Employee

## Re: EIGRp cost calculation

the correct formula can be found at :

http://www.cisco.com/warp/public/103/eigrp1.html#5

you're right about x = 0 for k5 = 0.

The thing is we just have 2 formula if you want.

One for k5 = 0 and one for k5 = 1

10exp7

Gold

## Re: EIGRp cost calculation

The formula in the white paper (above) is the right one. You can find it in different forms, but those other forms are either wrong, or they are simplifications of the above, based on the k values being default. Note that you actually have to do the right thing in the right order, and round down at every stage (always drop the remainders of the divides) to get exactly what the router gets.

For instance, if you have a 56k link, it's 10000000/56000 = 178, not 178.57....

:-)

Russ

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