EIGRP Metric Calculation Demystified When it comes to determining ...

EIGRP Metric Calculation Demystified 

When it comes to determining the EIGRP metric there seems to be many people who are 

confused in "how" it is actually calculated. I often times hear the following two questions, Can you 

just add the individual costs along the path to the destination like we do in OSPF? and Do we add the 

cost to the next-hop router to the reported distance (RD) as advertised by the next-hop router? The 

answer to both of these questions is absolutely and without a doubt, No. Why then is there so much 

confusion? I believe part of the problem lies in the inaccurate way it is referenced by many of the 

documentation sources available to readers. 

For example, in the old Cisco Press book titled, “CCNP Self Study: Building Scalable Cisco 

Internetworks (BSCI)”, by Catherine Paquet and Diane Teare, on page 362, it states the following in 

regard to the EIGRP metric: 

“The lowest-cost route is calculated by adding the cost between the next-hop router and the 

destination (referred to as the advertised distance [AD]) to the cost between the local router and the 

next-hop router. (The total is referred to as the feasible distance [FD].)” 

Upon first glance this seems correct, but this is clearly an incorrect statement regarding the 

EIGRP metric. In another example in the same book at the bottom of page 362, it gives the following 

definition for the feasible distance (FD). 

“FD or fd (feasible distance) - Equal to the sum of the costs of the links to reach network (a).” 

Again, an apparently inaccurate reference to the actual EIGRP metric. In addition, the examples 

that follow in the book, clearly show they are “adding” the individual link costs along the path from 

source to the destination to come up with the total EIGRP metric. An obvious oversight on the part of 

the author's resulting in an incorrect EIGRP calculation. 

Another source for the possible misunderstanding can be found in the new Cisco Press Book 

titled “Implementing Cisco IP Routing (ROUTE) Foundation Learning Guide”, by Diane Teare, on 

page 62, it states the following regarding the EIGRP metric: 

© BTS Communications, LLC Page 1


”The lowest-cost route is calculated by adding the cost between the next-hop router and the 

destination—referred to as the advertised distance (AD)—to the cost between the local router and the 

next-hop router. The sum of these costs is referred to as the feasible distance (FD).” 

In addition, on page 71 of the same book, the author states, 

”The AD is the EIGRP metric for an EIGRP neighbor router to reach a particular network. 

This is the metric between the next-hop neighbor router and the destination network. 

The FD is the EIGRP metric for this router to reach a particular network. This is the sum of the 

AD for the particular network learned from an EIGRP neighbor, plus the EIGRP metric to reach that 

neighbor (the metric between this router and the next-hop router).” 

Notice the author's use of the words “adding” and “sum” in the first reference as well as the use 

of “sum” in the second reference. I believe both of these references make an improper choice of the 

words to describe the calculation of the EIGRP metric and gives many readers an erroneous impression 

that you can simply “add” the AD of the neighboring router to the cost to reach the neighboring router. 

Resulting in a “sum” equal to the EIGRP metric. Again, this is incorrect and I will show this in an 

example later in the paper. 

Please, do not get me wrong, I am not trying to disrespect the authors' in any way. In fact, I am 

am very fond of both these author's and have several of their books in my own technical library. They 

are among my favorite list of authors'. I am merely trying to show a possible cause to the misguided 

and misunderstanding others may have regarding the EIGRP metric calculation. 

Furthermore, in the following Cisco document on “Enhanced Interior Gateway Routing 

Protocol (EIGRP)”, Document ID: 16406, it gives this definition for the feasible distance: 

”Feasible distance is the best metric along a path to a destination network, including the metric 

to the neighbor advertising that path. Reported distance is the total metric along a path to a 

destination network as advertised by an upstream neighbor.” 

Many people confuse the phrase “including the metric” in the above passage to mean that you 

“add” the metric to reach the next-hop neighbor to the reported distance (RD) of the upstream neighbor 



to arrive at the total metric along the path. Again, a seemingly misguided statement regarding the 

EIGRP metric, resulting in confusion and incorrect calculations. 

While it is true that the feasible distance (FD) is the total cost along a path from source to 

destination. It is erroneous to say the total metric is equal to the “sum” of the individual link costs or to 

say the total metric is equal to the cost to reach the next-hop neighbor “plus” the RD of the next-hop 

neighbor. You can verify this by using the EIGRP metric formula, shown below. 

METRIC=256∗[k1∗bandwidthk2∗bandwidth/256−load k3∗delay]∗[k5/reliabilityk4] 

Remember the default “k-values” are k1=k3=1 and k2=k4=k5 =0. Looking at the equation and 

the “k-values”, if k2=k4=k5 = 0, then mathematically this equation reduces to zero. Which we know is 

not what happens. Therefore, the EIGRP formula must be a “conditional” formula, a sort of “If-then” 

type scenario where if k5=0, then we set the last part of the equation to “1”. This results in the 

mathematically sound, often reduced EIGRP formula shown below. 

METRIC=256∗[k1∗bandwidthk3∗delay] 

Recall the EIGRP formula uses the minimum bandwidth (in kbps) along the path from source to 

destination and the total cumulative delay (in 10s of microseconds) along this same path from source to 

destination. For example, take the following network: 

Figure 1 – EIGRP Metric 

The metric (or cost) of each of the individual links can be calculated using the EIGRP formula. Shown 



below is a simplified version of the EIGRP formula above. 

METRIC=256∗BW Delay 

where BW = (10^7 / interface BW) and Delay = (total path delay / 10). Using the network diagram 

above and the EIGRP formula, will we prove the answer to the two opening questions is in fact “No” 

and disprove the often misguided, inaccurate statements found in so many publications regarding the 

EIGRP metric calculation. 

Step 1 - calculate the individual link metric for R1-R2. 

On the R1 to R2 link we are using an interface BW of 1544kbps and a delay of 20000 microseconds. 

The metric is calculated as follows: 

METRIC=256∗[10,000,000/1,54420,000/10] 

METRIC=256∗64762000 

METRIC=256∗8476=2169856 


Likewise, on the R2 to R3 serial link we calculate the metric to be 2169856. 

Step 3 - calculate the individual link metric for R3 to the destination network 10.1.1.0/24. 

The Fast Ethernet interface on R3 is calculated using an interface BW of 100Mbps and a delay of 100 

microseconds. The metric is 

Step 4 - adding the individual link metrics. 

METRIC=256∗[10,000,000/100,000100/10] 

METRIC=256∗10010 

METRIC=256∗110=28160 

Adding the individual link metrics from the steps above results in a total EIGRP metric of 4367872. 



METRIC=2169856216985628160=4367872 

Step 5 - calculate the metric using the EIGRP formula. 

Using the EIGRP formula to calculate the total metric from R1 to destination network 10.1.1.0/24 

results in metric of 2684416. In the above example the least BW is 1544kbps and the total cumulative 

delay is 20000 + 20000 + 100 = 40100. Using the EIGRP formula we get: 

METRIC=256∗[10,000,000/1,54440,100 /10] 

METRIC=256∗64764010 

METRIC=256∗10486=2684416 

Comparing the metrics calculated in Step 4 and Step 5, clearly shows these are not the same. 

Proving you can not simply “add” the individual link metrics to arrive at the total EIGRP metric. 

In addition, we can prove the total EIGRP metric is not equal to the cost to reach the next-hop 

neighbor “plus” the RD as advertised by the next-hop neighbor. Again, we can verify this using the 

EIGRP formula. 


As calculated in Step 1 above the cost or metric to reach the next-hop neighbor (R2 in our case) is 

2169856. 

Step 7 - calculate the FD for R2 to reach the destination network 10.1.1.0/24. 

The cost from R2 to destination network 10.1.1.0/24 is 2172416. This is the FD for R2 and is also the 

RD that is advertised to R1. The minimum BW is 1544kbps and the total cumulative delay is 20000 + 

100 = 20100. Using the EIGRP formula we get: 

METRIC=256∗[10,000,000/1,54420,100/10] 

METRIC=256∗64762010 



METRIC=256∗8486=2172416 

Step 8 - adding the RD of the next-hop neighbor to the cost to reach the next-hop neighbor. 

Adding the metric calculated in Step 6 to the metric calculated in Step 7 yields a total metric of 

4342272. 

METRIC=21698562172416=4342272 

Again, adding these two metrics together clearly shows the “sum” is not the same as the actual 

EIGRP metric we calculated in Step 5. 

So, in conclusion, we just proved that the total cost or metric in EIGRP is not equal to the “sum” 

of the individual link metrics nor is it equal to the RD of the next-hop neighbor “plus” the link metric to 

reach the next-hop neighbor. In all calculations of the EIGRP metric, you must use the EIGRP formula 

and calculate the metric from source to destination independently. Taking into consideration the 

minimum bandwidth along the path and the cumulative delay along the path. Meaning the metric for 

R2 to the destination network is calculated using the EIGRP formula and the minimum bandwidth and 

cumulative delay along the path from R2 to the destination network. Likewise, the metric for R1 must 

also be calculated using the EIGRP formula and the minimum bandwidth and cumulative delay along 

the path from R1 to the destination network. You cannot calculate R1's metric by taking the metric as 

seen by R2 and simply add the cost to reach R2. As we have shown in the above calculations, this does 

not result in the correct EIGRP metric calculation.

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