<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

By default EIGRP uses bandwidth and load to calculate its composite metric. Load and reliability can also be used, or the ratio at which bandwidth and delay are used can be changed, by modifying the metric weights. The default weighting of K1 and K3 mean that only bandwidth and delay are used. Like Anthony said the the calculation is as follows:

If k5 equals zero the second half of the equation is ignored.

The part that the documentation doesn't make clear enough is that the "bandwidth" is the inverse minimum bandwidth along the path multiplied by 2.56 * 1012, and delay is tens of microseconds multiplied by 256.

The weighting of the metrics can be seen from the show ip protocols command.

I think the simplest way of working it out (if K-values are default) is in two steps :

1) Change the "real" bandwidth to the inverse - which is 10,000,000/bw (kbits/s) - so for example if its an E1 then 10,000,000/2048. Once you have this number, forget the kbs value and only use this.

2) Do the following : metric = (bandwidth + aggregatd delay ) * 256

ta da! You have your metric. A lot simpler than trying to work out the full equation.. Go and test it on your labs ;-)

hth

(edit - as brian says above - the delay is in tens of microseconds - so depending on where you get the value you may need to divide by 10!)

## Comments

Great question - that part of the equation is only considered if K5 is NOT zero. If K5 is 0 (the default) - then this part of the equation is ignored.

Sorry still not clear. Even from my school days anything multiplied by zero = 0.

Am I being too mathematical about this? Cisco's use of the phrase equation I think may be throwing me?

No problem...let us say it this way...

The equation for EIGRP metric is:

Metric = [k1 * bandwidth + (k2 *

bandwidth)/(256 - load) + k3 * delay]

If K5 is not equal to 0, then Cisco uses the following equation:

Metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 *

delay] * [K5 / (reliability + K4)]

Makes better sense.

My school teachers can rest easy!

Thanks Anthony.

By default EIGRP uses bandwidth and load to calculate its composite

metric. Load and reliability can also be used, or the ratio at which

bandwidth and delay are used can be changed, by modifying the metric

weights. The default weighting of K1 and K3 mean that only bandwidth

and delay are used. Like Anthony said the the calculation is as

follows:

metric = [k1 * bandwidth + (k2 * bandwidth)/(256 - load) + k3 * delay]

* [k5/(reliability + k4)]

If k5 equals zero the second half of the equation is ignored.

The part that the documentation doesn't make clear enough is that the

"bandwidth" is the inverse minimum bandwidth along the path multiplied

by 2.56 * 1012, and delay is

of microsecondstensmultiplied by 256.

The weighting of the metrics can be seen from the show ip protocols

command.

Brian McGahan, CCIE #8593 (R&S/SP/Security)

[email protected]

Internetwork Expert, Inc.

http://www.InternetworkExpert.com

Toll Free: 877-224-8987 x 705

Outside US: 775-826-4344 x 705

Online Community: http://www.IEOC.com

CCIE Blog: http://blog.internetworkexpert.com

neza wrote:

I think the simplest way of working it out (if K-values are default) is in two steps :

1) Change the "real" bandwidth to the inverse - which is 10,000,000/bw (kbits/s) - so for example if its an E1 then 10,000,000/2048. Once you have this number, forget the kbs value and only use this.

2) Do the following : metric = (bandwidth + aggregatd delay ) * 256

ta da! You have your metric. A lot simpler than trying to work out the full equation.. Go and test it on your labs ;-)

hth

(edit - as brian says above - the delay is in tens of microseconds - so depending on where you get the value you may need to divide by 10!)