mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting an EIGRP network where route…
A network engineer is troubleshooting an EIGRP network where route summarization is configured. Router R1 has the 'ip summary-address eigrp 100 10.0.0.0 255.0.0.0' command on its interface facing R2. After the configuration, R2 loses connectivity to the 10.1.0.0/16 subnet, which is one of the component routes. The engineer checks the routing table on R2 and sees the summary route 10.0.0.0/8 but not the specific route. What is the most likely cause?
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 10.1.0.0/16 subnet is not included in the summary range because the summary mask is /8, but the subnet's network address is 10.1.0.0, which is within the range, but the EIGRP process may have a split-horizon issue or the component route is not in the EIGRP topology table.
In EIGRP, the summary address command suppresses the advertisement of more specific routes and generates the summary. However, if the summary route is not installed in the routing table (e.g., due to a missing component), the specific routes may still be suppressed, causing a black hole.
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 summary route 10.0.0.0/8 is being advertised with a metric of infinity, causing it to be ignored.
Why it's wrong here
Incorrect. A metric of infinity would prevent the route from being installed, but the specific routes would still be suppressed.
- ✗
The 10.1.0.0/16 subnet is not directly connected to R1, so it cannot be summarized.
Why it's wrong here
Incorrect. EIGRP can summarize routes learned from any interface.
- ✗
The summary address command was applied on the wrong interface, causing the summary to be sent out all interfaces, including the one facing the 10.1.0.0/16 subnet's origin.
Why it's wrong here
Incorrect. The summary is applied on a specific interface; it does not affect other interfaces.
- ✓
The 10.1.0.0/16 subnet is not included in the summary range because the summary mask is /8, but the subnet's network address is 10.1.0.0, which is within the range, but the EIGRP process may have a split-horizon issue or the component route is not in the EIGRP topology table.
Why this is correct
Correct. If the component route is not in the EIGRP topology table (e.g., due to a missing network statement or a passive interface), the summary route may still be generated, but the specific route is not advertised, causing loss of connectivity.
Visual reference
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.
Go deeper
Related to this question
About these practice questions
This 300-410 question is part of Courseiva's 1,966-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.