Metric formula EIGRP

[giovanni.valencia]

Hi,

Im preparing for CCNP ROUTE exam, and in the official book ciscopress the formula for EIGRP is something like this:

256 * ( ( 10.000.000 / slowest band along the path) +  cumulative delays)

But, in CCNP library before 2010 and the new release of exam,  the formula was this according to the official book:

256 * ( ( 10.000.000 / slowest band along the path) +  cumulative delays / 10 )

So, Is this an update in the formula or there is something wrong between the books?

thanks in advance.

regard,

Giovanni V.

[Peter Paluch]

Hi Giovanni,

The confusion between (cumulative delay/10) and (cumulative delay) is caused by the fact that the EIGRP formula itself counts the delay in non-intuitive units: tens of microseconds. The interface-level command delay accepts the value already in tens of milliseconds, and the value from that command is directly used in the formula, hence the format without dividing by 10.

On the other hand, the show interfaces command, for example, displays the delay simply in microseconds. Therefore, if we have units of microseconds, we have to convert them into units of tens of microseconds and only then use the delay in the formula, hence the format with the division by 10.

So in essence, both formats are correct but you have to take care in what units you express the delay in. The metric formula, in any case, uses units of tens of microseconds.

Best regards,

Peter

[giovanni.valencia]

Perfectly clear Peter!!

Thanks for your time and help.

best regards,

Giovanni