Question 1,627 of 1,958
hardMultiple ChoiceObjective-mapped
EIGRP Route Selection: Understanding Successor and Metric Comparison
An engineer is troubleshooting an EIGRP issue where a router is not learning a specific route from a neighbor. The engineer runs 'show ip eigrp topology all-links' and sees the route in the topology table with a feasible distance of 100 and a reported distance of 120. The neighbor's advertised distance is 80. The router's own computed distance to the network is 150. The route is not in the routing table. What is the most likely cause?
Quick Answer
The answer is that the route is not installed because the router already has a better successor route with a lower feasible distance of 100, making the computed distance of 150 a non-optimal path. In EIGRP route selection, the successor is the route with the best feasible distance (FD), which is the lowest metric from the router to the destination. Here, the topology table shows an FD of 100, which is lower than the router’s own computed distance of 150, so the router uses the FD 100 route as the successor and does not install the inferior path. On the ENCOR 350-401 exam, this tests your understanding of how EIGRP compares metrics and selects the successor—a common trap is confusing reported distance (the neighbor’s metric) with feasible distance (the router’s best metric). Remember: the successor is always the route with the lowest FD, not the lowest computed distance or advertised distance. A useful memory tip is “FD first: the smallest feasible distance wins the routing table.”
⚠ Common exam trap
Candidates often confuse the feasible distance (FD) with the computed distance of a specific path. Here, the FD is 100 from a different neighbor, but the route in question has a computed distance of 150—it is not the successor. The route is not installed because it is not the best path, not because of any feasibility condition issue.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route is not installed because its metric (150) is not the best metric; the router has another route with a lower metric (100).
The route in the topology table has a computed distance of 150 via the neighbor, but the feasible distance (FD) for this destination is 100, which is the best metric from another neighbor. EIGRP installs only the route with the lowest metric (the successor) into the routing table. Since the computed distance of 150 is higher than the FD of 100, this route is not the best and is not installed. Option C correctly identifies that the route is not installed because there is another route with a lower metric.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The route is a feasible successor, but the successor route is not present.
Why it's wrong here
Incorrect. A feasible successor must have a reported distance less than the feasible distance. Here, reported distance (120) is greater than feasible distance (100), so it is not a feasible successor.
- ✗
The route is not installed because the reported distance (80) from the neighbor is less than the feasible distance (100), but the router's computed distance (150) is higher.
Why it's wrong here
Incorrect. The reported distance from the neighbor is 80, which is less than the feasible distance of 100, so it meets the feasibility condition. However, the router's computed distance is 150, which is higher than the feasible distance, but that does not prevent installation. The issue is that the route is not the best.
- ✓
The route is not installed because its metric (150) is not the best metric; the router has another route with a lower metric (100).
Why this is correct
The route in the topology table has a computed distance of 150, which is higher than the feasible distance (FD) of 100. EIGRP only installs the successor route (lowest metric) into the routing table, so this route is not installed because it is not the best path.
- ✗
The route is not installed because EIGRP is configured for stub routing, which prevents learning routes.
Why it's wrong here
Incorrect. Stub routing only affects query propagation, not route learning. The route is in the topology table, so it is learned.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Same concept, more angles
1 more way this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer is troubleshooting an EIGRP issue in a large enterprise network. Two routers, R1 and R2, are connected via a T1 link. R1 is learning a route to 10.0.0.0/8 from R2 with a metric of 28160, but the same route is also learned from another neighbor with a metric of 26880. The engineer notices that the route from R2 is not being installed in the routing table. What is the most likely cause?
medium- A.The route from R2 is a feasible successor, so it is not installed in the routing table.
- B.EIGRP is using unequal-cost load balancing, so the higher metric route is not used.
- ✓ C.The route with metric 28160 is not installed because EIGRP selects the route with the lowest metric.
- D.The route from R2 is a summary route, so it is not installed in the routing table.
Why C: C is correct because EIGRP installs only the route with the best (lowest) metric into the routing table. The route from R2 has a metric of 28160, while the other neighbor advertises the same route with a metric of 26880. Since 26880 is lower, R1 selects that route as the successor and does not install the higher-metric route from R2.
Last reviewed: Jun 24, 2026
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