We often configure EIGRP and move on, but do we ever pause and ask — how does EIGRP decide which path is the best? The answer lies in its metric calculation — the “math” behind routing decisions.
Trust me, once you understand EIGRP’s metric logic, you’ll troubleshoot smarter, design better, and even pass your certifications with confidence. Let’s keep it hands-on and practical as always.
Table of Contents
Theory in Brief – What is EIGRP Metric?
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco-proprietary, advanced distance-vector routing protocol. It’s considered a hybrid because it uses some link-state behavior like DUAL (Diffusing Update Algorithm) and supports fast convergence.
But what really powers EIGRP is its metric calculation, which determines the “best” route to a destination.
Default EIGRP Metric Formula
EIGRP uses this formula to calculate the metric:
Metric = 256 × ((10⁷ / min bandwidth in kbps) + cumulative delay in tens of microseconds)
That’s the default metric when only bandwidth and delay are considered. Reliability and Load are optional and disabled by default.
Components of the Metric:
- Bandwidth – Minimum bandwidth of the path
- Delay – Cumulative delay across the entire path
- Reliability – Optional; based on interface reliability
- Load – Optional; based on traffic load
- MTU – Not used in metric but propagated
EIGRP allows fine control using K-values (K1
to K5
). By default:
K1 = 1
(Bandwidth)K3 = 1
(Delay)- Others = 0
This means only bandwidth and delay are factored in by default.
Example
If a path has:
- Bandwidth = 1000 kbps
- Delay = 20000 microseconds
Then:
- Metric = 256 × ((10⁷ / 1000) + 2000) = 256 × (10000 + 2000) = 3,072,000
This number is what EIGRP uses to compare routes. Lower metric = better route.
Key Parameters
Parameter | Used in Metric? | Description | Default in Calculation |
---|---|---|---|
Bandwidth | Yes | Slowest link in kbps | K1 = 1 |
Delay | Yes | Total delay across all hops (μs/10) | K3 = 1 |
Reliability | Optional | Measure of link stability (1–255) | K2 = 0 |
Load | Optional | Dynamic interface traffic | K4/K5 = 0 |
MTU | Not used | Propagated but not metric-influencing | – |
Pros and Cons of EIGRP Metric System
Pros | Cons |
---|---|
Intelligent path selection based on real values | Complex formula for beginners |
Allows fine-tuning using K-values | Changing K-values must match on all routers |
Fast convergence using DUAL algorithm | Cisco proprietary (less cross-vendor support) |
Supports unequal-cost load balancing (variance) | Metric may not reflect real-time traffic conditions |
Essential CLI Commands
Command | Purpose |
---|---|
show ip eigrp topology | View route metrics and topology info |
show ip route eigrp | Check EIGRP entries in routing table |
show ip eigrp interfaces | Show interfaces participating in EIGRP |
show ip protocols | View K-values and routing info |
show running-config | Confirm bandwidth, delay settings |
interface x/x delay 1000 | Adjust delay on interface |
bandwidth 1000 | Change bandwidth to influence metric |
router eigrp 100 variance 2 | Enable unequal-cost load balancing |
Real-World Use Case
Scenario | How EIGRP Metric Helps |
---|---|
Branch office connected via MPLS and broadband | EIGRP chooses MPLS due to better delay/bandwidth |
Data center links with different speeds | Ensures primary path goes via 10G instead of 1G |
ISP failover with floating static + EIGRP | EIGRP adapts routes, static kicks in if EIGRP fails |
Unequal link paths (10 Mbps vs 100 Mbps) | Use variance to utilize both paths smartly |
Wireless vs Wired WAN paths | Delay/bandwidth helps prioritize reliable wired paths |
EVE-NG LAB – See the Metric in Action
Topology

- R1 connects to R3 via R2 and R4 (different delays/bandwidths)
- EIGRP running on all routers
Configuration Snippet
On All Routers:
router eigrp 100
network 192.168.0.0
On Interfaces (to simulate metric difference):
interface g0/1
bandwidth 1000
delay 100
interface g0/2
bandwidth 100
delay 1000
Use:
show ip eigrp topology
…to observe differences in feasible distance.
Test:
- Ping from R1 to R3
- Shut one path, observe route change
- Use
variance 2
on R1 to enable unequal load balancing
Troubleshooting Tips
Symptom | Cause | Solution |
---|---|---|
EIGRP not choosing preferred path | Delay/Bandwidth imbalance | Tune interface metrics |
No EIGRP neighbor | K-values mismatch or ACL | Use show ip protocols , check configs |
High metric shown unexpectedly | Wrong interface delay/bandwidth | Use show interface , adjust values |
Unequal paths not used | Variance not set | Use variance under router config |
Route not appearing in RIB | Feasibility condition not met | Check AD and FD, adjust metrics if needed |
Frequently Asked Questions (FAQs)
1. What is EIGRP metric, and why is it important in route selection?
Answer:
EIGRP (Enhanced Interior Gateway Routing Protocol) uses a composite metric to determine the best path to a destination. This metric is calculated using several parameters such as bandwidth, delay, load, and reliability. Among these, bandwidth and delay are used by default. The lower the metric, the better the route. This calculation helps EIGRP intelligently choose the most optimal path, ensuring efficient and loop-free routing in enterprise networks.
2. What are the default K-values used in EIGRP metric calculation?
Answer:
EIGRP uses a formula with K-values (constants) to determine how different parameters influence the metric. The default K-values are:
- K1 = 1 (Bandwidth)
- K2 = 0 (Load)
- K3 = 1 (Delay)
- K4 = 0 (Reliability)
- K5 = 0 (Reliability)
With these defaults, only bandwidth and delay are factored into metric calculation, making it simpler and more stable.
3. What is the EIGRP metric formula with default K-values?
Answer:
With default K-values (K1=1, K3=1, others = 0), the metric formula becomes:
Metric = [(10^7 / Minimum Bandwidth in kbps) + Sum of Delays in tens of microseconds] * 256
This means EIGRP prefers higher bandwidth and lower cumulative delay when selecting routes.
4. How is bandwidth used in EIGRP metric calculation?
Answer:
EIGRP uses the minimum bandwidth along the path from source to destination. It converts this to a metric by using the formula 10^7 / bandwidth in kbps
. Lower bandwidth increases the metric value, making the path less preferred. For instance, a 100 Mbps link gives a better (lower) metric than a 10 Mbps link.
5. How is delay calculated and included in the metric?
Answer:
EIGRP adds the cumulative delay of all outgoing interfaces along the path. Delay is measured in microseconds but converted to tens of microseconds for metric calculation. For example, a delay of 10000 microseconds becomes 100. This total delay is added to the bandwidth part before multiplying the result by 256.
6. Can load and reliability affect the EIGRP metric?
Answer:
Technically, yes – EIGRP supports load and reliability as metric components. However, since their K-values (K2, K4, and K5) are set to 0 by default, they are not included in the calculation. If these values are manually changed, they can influence route selection, but doing so may introduce instability and complexity in the network.
7. How do I view the EIGRP metric values on a Cisco router?
Answer:
Use the following CLI command:
show ip route eigrp
Or to view detailed metric components per route:
show ip eigrp topology
This command shows the feasible distance (FD), bandwidth, delay, reliability, and load for each route in the EIGRP topology table.
8. Can I change the delay or bandwidth manually to influence EIGRP metrics?
Answer:
Yes. You can manipulate interface delay and bandwidth to influence EIGRP’s route selection without modifying K-values. For example:
interface GigabitEthernet0/0
bandwidth 10000
delay 100
This is commonly used in enterprise networks for traffic engineering or policy-based routing behavior.
9. What is the feasible distance and how is it related to metric calculation?
Answer:
The feasible distance (FD) is the total metric from the local router to the destination network via a particular path. It is calculated using the EIGRP metric formula. The FD is stored in the EIGRP topology table and is used to determine the best route. The lowest FD becomes the successor (primary route).
10. Is it recommended to change the K-values in EIGRP?
Answer:
In most cases, no. Changing K-values can lead to inconsistent metrics across routers, causing instability or routing loops if not done properly on all EIGRP routers. It’s best practice to leave K-values at their defaults (K1=1, K3=1, others=0) and instead tweak bandwidth or delay per interface if you need to influence routing behavior.
YouTube Link
Watch the Complete CCNP Enterprise: EIGRP Metric Calculation – Understand the Brain Behind Route Selection Lab Demo & Explanation on our channel:
Final Thoughts
EIGRP’s metric may seem complex at first, but once you understand the logic, you gain predictable control over your network behavior. You’ll no longer be confused why one route is chosen over another — because now you can calculate and influence it.
As always, don’t just read — build this lab in EVE-NG, break things, and learn how to fix them. That’s how real engineers grow.
Final Note
Understanding how to differentiate and implement EIGRP Metric Calculation – Understand the Brain Behind Route Selection is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.
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