- 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.
EIGRP Summary Route Suppression and Administrative Distance
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?
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."
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 with an administrative distance of 5 creates a summary route (10.0.0.0/22) in the EIGRP topology table that is more preferred than the specific /32 route (10.0.1.1) learned via EIGRP with a default distance of 90. This causes the summary to be installed in the routing table, and the specific /32 route is suppressed because the summary is considered a better path, leading to intermittent loss of reachability to the loopback.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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: answer the scenario, not the keyword
Cisco often tests the interaction between summary-address and administrative distance, where candidates mistakenly think the summary only affects routing table size or advertisement, but the trap is that a lower AD on the summary can suppress more specific routes and cause reachability problems.
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
EIGRP's summary-address command with an administrative distance (AD) of 5 creates a local summary route with a lower AD than the default internal EIGRP distance of 90, making it more trustworthy. This summary route is installed in the routing table as a connected-like route (via Null0), and EIGRP will not advertise the more specific /32 route because the summary covers it, effectively blackholing traffic to the loopback unless a more specific route exists. In real-world scenarios, this misconfiguration can cause intermittent connectivity issues when the summary route is preferred over the specific route, especially during network convergence.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
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 with an administrative distance of 5 creates a summary route (10.0.0.0/22) in the EIGRP topology table that is more preferred than the specific /32 route (10.0.1.1) learned via EIGRP with a default distance of 90. This causes the summary to be installed in the routing table, and the specific /32 route is suppressed because the summary is considered a better path, leading to intermittent loss of reachability to the loopback.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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