- A
The summary-address command uses an administrative distance of 5, which is lower than the default EIGRP internal distance of 90, causing the summary to override the specific /32 route.
The summary route with distance 5 is installed in the routing table, and EIGRP does not install the more specific route because the summary is already present with a better distance.
- B
The network statement on R1 does not include the loopback interface of R2, preventing the route from being advertised.
Why wrong: The network statement covers the 10.0.0.0/8 range, so all subnets including the loopback should be advertised.
- C
The summary-address command is misconfigured; the mask should be 255.255.255.252 instead of 255.255.252.0.
Why wrong: The mask 255.255.252.0 is correct for summarizing a /22 block; the issue is the distance, not the mask.
- D
R2 is not configured with EIGRP, so it cannot receive the route from R1.
Why wrong: The scenario states R2 is a router, and the topology table on R1 shows the summary, so EIGRP is running.
Quick Answer
The answer is that the summary-address command with an administrative distance of 5 causes the summary route to suppress the specific /32 loopback route. In EIGRP, a summary route created locally with the `summary-address` command is installed in the routing table with a default administrative distance of 5, which is significantly lower than the default EIGRP internal distance of 90. Because the router prefers the lower-distance summary route pointing to Null0, it suppresses the more specific /32 route learned from a neighbor, even if that specific route appears in the topology table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how EIGRP summary route suppression interacts with administrative distance—a common trap is assuming the summary only affects advertisement, not local route selection. Remember: a summary with a distance of 5 is like a "super admin" that overrides any specific route, so the fix is to either remove the summary or adjust its distance. Memory tip: "Distance 5 keeps the specific route from arriving."
300-410 Device Management Practice Question
This 300-410 practice question tests your understanding of device management. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A large enterprise network is experiencing intermittent loss of reachability to a loopback interface on Router R2 from Router R1. R1 has the following relevant configuration: router eigrp 100, network 10.0.0.0 0.255.255.255, summary-address 10.0.0.0 255.255.252.0 5. R2 shows: 'show ip eigrp topology all-links' includes 10.0.0.0/22 as a summary route via Null0, but the specific /32 loopback 10.0.1.1 is not in the topology table. What is the root 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 summary-address command uses an administrative distance of 5, which is lower than the default EIGRP internal distance of 90, causing the summary to override the specific /32 route.
The summary-address command on R1 creates a local summary route to Null0, but the administrative distance of 5 (default for EIGRP summary) causes the summary to be preferred over more specific routes learned from neighbors. The specific /32 is suppressed because the summary is installed in the routing table with a better distance, blocking the more specific route from being installed. The fix is to adjust the summary distance or not summarize.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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-address command uses an administrative distance of 5, which is lower than the default EIGRP internal distance of 90, causing the summary to override the specific /32 route.
- ✗
The network statement on R1 does not include the loopback interface of R2, preventing the route from being advertised.
Why it's wrong here
The network statement covers the 10.0.0.0/8 range, so all subnets including the loopback should be advertised.
- ✗
The summary-address command is misconfigured; the mask should be 255.255.255.252 instead of 255.255.252.0.
Why it's wrong here
The mask 255.255.252.0 is correct for summarizing a /22 block; the issue is the distance, not the mask.
- ✗
R2 is not configured with EIGRP, so it cannot receive the route from R1.
Why it's wrong here
The scenario states R2 is a router, and the topology table on R1 shows the summary, so EIGRP is running.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
The scenario states R2 is a router, and the topology table on R1 shows the summary, so EIGRP is running.
Scenario analysis trap
The scenario states R2 is a router, and the topology table on R1 shows the summary, so EIGRP is running.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The summary-address command uses an administrative distance of 5, which is lower than the default EIGRP internal distance of 90, causing the summary to override the specific /32 route. — The summary-address command on R1 creates a local summary route to Null0, but the administrative distance of 5 (default for EIGRP summary) causes the summary to be preferred over more specific routes learned from neighbors. The specific /32 is suppressed because the summary is installed in the routing table with a better distance, blocking the more specific route from being installed. The fix is to adjust the summary distance or not summarize.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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