hardMultiple ChoiceObjective-mapped
300-410 Router R1 and R2 are running EIGRP Practice Question
Router R1 and R2 are running EIGRP. R1 has a route to 172.16.0.0/16 with AD 90. R2 redistributes a static route for 172.16.0.0/16 into EIGRP with a route-map that sets the administrative distance to 85. R1 learns the redistributed route with AD 85 and installs it, overriding the original internal route. However, R1's 'show ip route 172.16.0.0' shows the route via R2 with AD 85, but pings to 172.16.1.1 fail. 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 redistributed route is a summary route that does not contain the specific subnet 172.16.1.0/24, causing packets to be dropped.
Setting AD to 85 makes the redistributed route preferred over the internal route (AD 90). However, the redistributed route might have a less specific prefix (e.g., 172.16.0.0/16) while the internal route might have a more specific prefix (e.g., 172.16.1.0/24) that is now hidden. The ping fails because the redistributed route is a summary that does not have a valid next hop for the specific subnet. The correct answer is that the redistributed route is a summary that does not include the specific subnet, causing blackholing.
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 redistributed route is a summary route that does not contain the specific subnet 172.16.1.0/24, causing packets to be dropped.
Why this is correct
The summary route may point to a null interface or a next hop that does not have the specific route.
- ✗
The route-map set distance 85 is ignored because EIGRP internal routes always have AD 90.
Why it's wrong here
Route-map can change AD for redistributed routes.
- ✗
R1's EIGRP process has a distribute-list blocking the redistributed route.
Why it's wrong here
The route is installed.
- ✗
The redistributed route has a higher metric than the internal route, but AD overrides metric.
Why it's wrong here
AD is lower, so it is installed regardless of metric.
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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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.