Simple question on EIGRP metric

Unanswered Question
Oct 13th, 2009

At least it OUGHT to be simple

I have a little EIGRP lab up and running, one entry in my topology table reads:

P, 1 successors, FD is 2297856

--via (2297856/128256), Serial0

So I'm trying to make sure I understand the metric calculation (using default K values). The sum of (10,000,000 divided by BW in kbps, plus delay (in 10's of microseconds)) multiplied by 256.

So I took the FD, 2297856, divided by 256, and got 8976.

Delay on Serial0 (the peer at S0 is the last stop; there are no other interfaces in the path) is 20000 microsec. That's 2000 tens of usec, so I subtract and get 6976.

So far so good. Declared BW on the link is good ol' 1544 kbps. I divide that into 10,000,000 and get 6476.6839bla bla bla.

Except I was expecting something more in the neighborhood of the 6976 I was working with a moment ago. What have I missed? Why have I missed it by 500?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Istvan_Rabai Wed, 11/11/2009 - 07:40


The calculation of the EIGRP metric is based on the SUM of delays along the path.

Look at the interface where the network is configured.

I suppose it has a 5000 microseconds delay that should be calculated into the formula.

So the sum of delays will be 25000 microseconds, which is 2500 tens of microseconds.

After all, the packets have to be transmitted over that interface as well to reach the destination, so its delay must be calculated into the metric.




This Discussion