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300-410 Practice Question: Is troubleshooting a connectivity issue between…
A network engineer is troubleshooting a connectivity issue between two branches connected via a WAN link. Router R1 (10.1.0.0/16) is summarizing its directly connected subnets (10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24) as a single 10.1.0.0/16 route to Router R2 via EIGRP. Users at R2 report that they cannot reach the 10.1.4.0/24 subnet, which was recently added to R1. What is the most likely cause of the problem?
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 new subnet 10.1.4.0/24 was not advertised because the summary address command suppresses more specific routes, but the summary itself is not being generated due to a missing network statement under the EIGRP process.
The summary route 10.1.0.0/16 includes the new subnet 10.1.4.0/24, but the issue indicates that the summary is not being updated or is too broad, causing a mismatch. The most likely cause is that the summary address was configured manually and does not automatically include new subnets unless the summary range is adjusted.
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 10.1.0.0/16 was configured manually, and the new subnet 10.1.4.0/24 is not within the summary range because the mask is too specific.
Why it's wrong here
Incorrect because 10.1.4.0/24 is within the 10.1.0.0/16 range. The summary should include it.
- ✓
The new subnet 10.1.4.0/24 was not advertised because the summary address command suppresses more specific routes, but the summary itself is not being generated due to a missing network statement under the EIGRP process.
Why this is correct
Correct. In EIGRP, a manually configured summary address suppresses the advertisement of more specific routes and generates the summary only if the component routes exist. If the new subnet is not in the EIGRP network, the summary may not be generated or the specific route is missing.
- ✗
The WAN link is down, causing R2 to lose the summary route.
Why it's wrong here
Incorrect. The symptom is specific to the new subnet; other subnets are reachable, so the link is likely up.
- ✗
The engineer forgot to configure the summary address on the interface facing R2 for the new subnet.
Why it's wrong here
Incorrect. A single summary address covers all subnets; no additional summary is needed for the new subnet.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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