EIGRP Metric Calculation

[surendrasinghtanwar667]

Hello everyone,

While learning EIGRP, I encountered a challenge regarding metric calculation. I understand that each router calculates the Feasible Distance (FD) to reach a destination. As part of this process, each router first calculates the cost to reach the next hop. Once the next hop metric is determined, it adds the Reported Distance (RD) to compute the total Feasible Distance (FD).

However, my question is: How is the next hop metric calculated? Additionally, where can I see this next hop metric in the router's output?

Any clarification on this would be greatly appreciated!

[ammahend]

By default, EIGRP calculates the cost to reach neighbor using just bandwidth and delay

Let’s say between Router A and its neighbor Router B:

Bandwidth: 1000 Kbps
Delay: 5000 microseconds

using the formula

Total metric (Cost_to_Neighbor): (10,000)+(5000/10)×256=2,688,000

more details here

[surendrasinghtanwar667]

But i guess the formula you mentioned is to calculate the FD (Feasible Distance)

[MHM Cisco World]

I think you talk about AD and FD

Check below youtube is very good 

https://youtu.be/CCAuPSPMRiY?si=QrRkYYjOMx6BUGIu

[paul driver]

Hello
Eigrp require neighbours adjacency to form before any routes are calculated, thus if a rtr has multiple adjacencys then the best next hop (successor) is  calculated with eigrp metrics be it classic or wide metric.

lease review this

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@surendrasinghtanwar667 wrote:

Hello everyone,

While learning EIGRP, I encountered a challenge regarding metric calculation. I understand that each router calculates the Feasible Distance (FD) to reach a destination. As part of this process, each router first calculates the cost to reach the next hop. Once the next hop metric is determined, it adds the Reported Distance (RD) to compute the total Feasible Distance (FD).

However, my question is: How is the next hop metric calculated? Additionally, where can I see this next hop metric in the router's output?

Any clarification on this would be greatly appreciated!

---

Eigrp requires neighbour adjacency to for any nexthop (successor) to be calculated, if a eigrp rt has multiple adjacencies then the metric calculation is performed be it with classic or wide metric, with wide metric now being preferred via named eigrp.

Please review this post

[surendrasinghtanwar667]

i am saying if any router calculate the feasible distance to reach the distance and it will calculate the local cost and add the advertised distance or reported distance from the neigbhor router so how eigrp calculate the local cost to reach the distance i am asking that ????

As you can see the screenshot =, my question is how Router 2 have calculate this value 284160 I know this feasible distance but i wan't to know that how eigrp calculate the local cost to reach the next hop ???

[surendrasinghtanwar667]

https://www.practicalnetworking.net/stand-alone/eigrp-terminology/

see in this article he has mentioned one line 

[MHM Cisco World]

R1-R2-R3

R1 calculate cost to R2 with metric formula show above' 

R2 Send cost to R3 as FD to R1

So R1  now have cost+FD

MHM

[David Ruess]

Hello,

EIGRP uses two values (by default) to calculate its Feasible Distance (FD) which is LOWEST BW and CUMULATIVE DELAY. These are important distinctions to help you understand the calculation.

EIGRP sends its update packets with the lowest BW its seen so far. So, when an EIGRP router receives an update, it will see the BW in it and compare it to the interface BW it received it on. If it's the same or higher than the one in the update it does nothing. If the BW on the interface is lower, then it updates the update to replace the current lowest BW and sends to its neighbors downstream where they do the same thing. 

Simultaneously it adds the delay to the delay seen in the update and it does pass that along to neighbors. Regardless of higher or lower as its cumulative meaning you keep adding the values along the path.

So to wrap it up the metric calculation is the lowest BW on the entire path and the cumulative delay for all interfaces the routes needs to take. Then the device locally computes its metric.

Keep in mind another important distinction. The Feasible Distance that is calculated is NOT sent in updates. The only thing that is sent is the lowest BW thats seen along the path AND the cumulative delay added at each incoming interface. Each router will receive the update and inspect it. It will add its interface delay of the incoming interface and if the BW is the lowest seen so far it will update that. Then it will perform a local calculation and get its metric. It will then send the update with the BW and new delay.

Hope this helps

-David

[surendrasinghtanwar667]

ohkk so there is no local metric to reach the next hop as mentioned in the article which i have mentioned ?? sorry David i am asking the same question but i have invested a lot of time and i stucked understanding eigrp metric so can you please help me out and please correct me if i am wrong at any point 

[David Ruess · Accepted solution]

Apologies. I'd like to make a slight correct to my statement above. I was confused on your example using terms like cost. The neighbor does send its metric also known as the Reported Distance (RD) or Advertised Distance (AD). But the router still locally computes its own Feasible Distance (FD) based on the BW and the Delay as mentioned above. Let me try to help clarify the other aspects.

The "local" metric to reach the next hop would be the added interface Delay and BW associated with the incoming interface with a caveat. It will only use its interface BW if its the lowest in the path. If its not then it will use the Bandwidth seen in the received update. It will then add its interface delay to the delay seen in the update. It will then calculate its metric to the route locally using those two values and putting them into the EIGRP metric Formula.

-David 

[surendrasinghtanwar667]

Thank you david now i have understand, actually i was confused from past few days how does eigrp metric work thank you once again 

[MHM Cisco World]

As I mention above 

MHM

[MHM Cisco World]

the cisco use FD and AD and many term make engineer confuse 
but in reality the FD and AD calculate with same formula  

the different in term is come from AD is calculate of metric done by router itself and FD is metric calculate done by router neighbor

there are many online calculator (I prefer use it for eigrp metric) 
below is how R1 calculate the metric to LO4.4.4.4 in R4  

NOTE:- the AD use in RIB not FD, FD use only to select the path and to prevent Loop

MHM

EIGRP Metric Calculator (53bits.co.uk)

[tyler87432f]

EIGRP (Enhanced Interior Gateway Routing Protocol) uses a composite metric to determine the best path to a destination. The metric calculation considers five key factors: bandwidth, delay, load, reliability, and MTU (though MTU does not affect route selection). The formula primarily focuses on the lowest bandwidth and cumulative delay along the path. By default, EIGRP uses the following formula:

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