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Enhanced Interior Gateway Routing Protocol (EIGRP) makes routing decisions by calculating a composite metric. For Cisco administrators, understanding how EIGRP metrics work is essential for predicting route selection, troubleshooting unexpected paths, and tuning the network for better performance. While many engineers know that bandwidth and delay matter, fewer understand how the full calculation works, what K-values do, and why feasible successors depend on these values.
This guide explains EIGRP metrics in practical terms. You will learn which interface values affect route selection, how the classic formula is built, how to verify metric values from the CLI, and what to watch for when modifying interfaces in production.
EIGRP uses a composite metric rather than a simple hop count. In the default configuration, the metric is calculated from the minimum bandwidth along the path and the cumulative delay across the path. This makes EIGRP more aware of real link characteristics than protocols that only count routers.
By default, Cisco EIGRP uses these K-values:
Because only K1 and K3 are enabled by default, classic EIGRP metric calculation is normally based on bandwidth and delay only.
When K1 = 1 and K3 = 1, the classic EIGRP metric is effectively:
metric = 256 * ( (10^7 / minimum bandwidth in Kbps) + sum of delays in tens of microseconds )
There are two important details here:
This means a single slow interface can dominate the path metric even if the rest of the route is fast.
EIGRP does not measure real-time throughput for path selection. Instead, it uses the configured interface bandwidth value. That value is often manually set by administrators and may not always match the physical link speed.
For example, if one path includes a 10 Mbps link and another path stays at 100 Mbps or higher end-to-end, the path with the 10 Mbps bottleneck will usually have the worse metric, even if both paths have the same hop count.
You can check interface bandwidth with:
show interfaces GigabitEthernet0/0 show ip eigrp interfaces detail
If the configured bandwidth is inaccurate, EIGRP path selection may not match the real design intent.
Delay is the second major input in the default metric calculation. Unlike bandwidth, delay is cumulative across the path. Each interface contributes a delay value, and EIGRP adds them together before calculating the final metric.
Delay becomes especially important when competing paths have similar bandwidth. In that case, the route with lower total delay usually wins.
Delay is visible in interface output:
show interfaces GigabitEthernet0/1
You can also tune delay administratively to influence path selection without changing the bandwidth statement. This is a common technique when you want traffic engineering behavior while preserving QoS or management assumptions tied to bandwidth.
Assume Router A can reach 192.168.50.0/24 over two paths:
Using the default classic formula:
Path 1
10^7 / 100000 = 100 100 + 200 = 300 300 * 256 = 76800
Path 2
10^7 / 10000 = 1000 1000 + 100 = 1100 1100 * 256 = 281600
Even though Path 2 has lower delay, the much lower minimum bandwidth causes a far worse EIGRP metric. Router A selects Path 1.
K-values determine which variables participate in the metric calculation. In most environments, administrators leave them at their defaults. Changing K-values is rare and must be done consistently across EIGRP neighbors. If routers do not match, they will not form or maintain EIGRP adjacencies correctly.
You can verify them with:
show ip protocols
In production networks, changing K-values is usually unnecessary and can introduce avoidable complexity. Interface bandwidth and delay tuning are far more common and easier to reason about.
To understand EIGRP metrics fully, you also need to understand the values EIGRP stores in the topology table:
The route with the lowest feasible distance becomes the successor route and is installed in the routing table. A backup route can become a feasible successor if it meets the feasibility condition, meaning the neighbor’s reported distance is lower than the local router’s current feasible distance.
This is one of the reasons EIGRP converges quickly. If a feasible successor already exists, the router can switch to it immediately when the primary path fails.
EIGRP supports both equal-cost and unequal-cost load balancing. Equal-cost balancing happens automatically up to the configured maximum paths. Unequal-cost balancing requires the variance command.
variance
Example:
router eigrp 100 variance 2
This allows EIGRP to install additional feasible routes whose metrics are within the variance multiplier of the best route, provided they satisfy feasibility requirements. This feature is useful in WAN environments where backup circuits are slower but still acceptable for load sharing.
Traditional EIGRP metric calculations are often called classic metrics. On modern high-speed networks, classic metrics may not provide enough granularity for very fast links. Cisco introduced wide metrics to improve scaling and precision, especially in larger or faster environments.
In many enterprise deployments, you will still encounter classic metrics. That means engineers should understand both the original formula and the operational impact of bandwidth and delay values on interfaces.
These Cisco IOS commands are the most useful when validating EIGRP path selection and metric inputs:
show ip route eigrp show ip eigrp topology show ip eigrp topology all-links show ip protocols show ip eigrp neighbors show ip eigrp interfaces detail show interfaces
These commands help answer critical questions:
If EIGRP selects an unexpected path, use a structured approach:
show ip route eigrp
show ip eigrp topology
In many cases, the root cause is not EIGRP itself but an interface bandwidth statement inherited from an old deployment or a delay value changed for traffic engineering.
EIGRP metrics are straightforward once you break them into their key parts. By default, Cisco EIGRP chooses routes based on minimum bandwidth and cumulative delay, wrapped into a composite metric. K-values control which variables participate, while feasible distance and reported distance drive route selection and fast failover behavior.
For day-to-day network operations, the most important skills are knowing how bandwidth and delay influence path selection, understanding how to read the EIGRP topology table, and using IOS verification commands to confirm why a route won. Master those basics, and EIGRP becomes much easier to predict and troubleshoot.