- A
EIGRP will automatically summarize 192.168.1.0 to 192.168.0.0/16.
Why wrong: Auto-summary is disabled, so no classful summarization occurs.
- B
EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes.
With no auto-summary, subnets are advertised without summarization.
- C
EIGRP will only advertise the classful networks 192.168.0.0/16 and 10.0.0.0/8.
Why wrong: Auto-summary is disabled, so classful summarization does not occur.
- D
EIGRP will not form neighbor adjacencies due to missing network mask.
Why wrong: Network statements without a mask use the classful address, which is valid for EIGRP.
Question 1,595 of 2,152
EIGRP No Auto-Summary: Advertising Exact Prefixes
This 300-410 practice question tests your understanding of eigrp troubleshooting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Given the following EIGRP configuration on Router R2:
router eigrp 200 network 192.168.1.0 network 10.0.0.0 no auto-summary
Which statement is true about the operation of EIGRP?
Quick Answer
The answer is that EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes. This is correct because the `no auto-summary` command disables EIGRP’s default behavior of summarizing networks at their classful boundaries—for example, converting a /24 subnet back to its Class C /24 or a /8 to its Class A /8. With auto-summary enabled, EIGRP would advertise 192.168.1.0 as 192.168.0.0/16 and 10.0.0.0 as 10.0.0.0/8, but `no auto-summary` forces the router to advertise the exact prefix lengths configured under the `network` statements. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of classful versus classless routing behavior in EIGRP, often appearing in scenario-based questions where a missing `no auto-summary` causes unexpected route summarization and suboptimal path selection. A common trap is assuming EIGRP always advertises subnets exactly; remember that auto-summary is enabled by default in classic EIGRP, so you must explicitly disable it for discontiguous networks. Memory tip: “No auto-summary means no classful boundaries—advertise the exact subnet you see.”
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
✓
EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes.
The 'no auto-summary' command disables automatic classful summarization in EIGRP. Therefore, EIGRP advertises the exact subnet masks configured under the 'network' statements: 192.168.1.0/24 and 10.0.0.0/8, rather than summarizing them to their classful boundaries (192.168.0.0/16 and 10.0.0.0/8). This ensures that all subnets are advertised with their original prefix lengths.
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.
- ✗
EIGRP will automatically summarize 192.168.1.0 to 192.168.0.0/16.
Why it's wrong here
Auto-summary is disabled, so no classful summarization occurs.
- ✓
EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes.
Why this is correct
With no auto-summary, subnets are advertised without summarization.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
EIGRP will only advertise the classful networks 192.168.0.0/16 and 10.0.0.0/8.
Why it's wrong here
Auto-summary is disabled, so classful summarization does not occur.
- ✗
EIGRP will not form neighbor adjacencies due to missing network mask.
Why it's wrong here
Network statements without a mask use the classful address, which is valid for EIGRP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'no auto-summary' is the default behavior in all IOS versions, when in fact it must be explicitly configured in older versions (pre-15.0) to avoid classful summarization.
Detailed technical explanation
How to think about this question
EIGRP's 'network' command uses a wildcard mask (defaulting to 0.0.0.0 for classful networks) to enable EIGRP on interfaces. With 'no auto-summary', EIGRP advertises the exact prefix length of the interface IP, which is critical in discontiguous network designs to prevent routing black holes. For example, without 'no auto-summary', a router with 10.1.1.0/24 and 10.2.2.0/24 would advertise only 10.0.0.0/8, losing subnet specificity.
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 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.
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.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: EIGRP will advertise 192.168.1.0/24 and 10.0.0.0/8 as exact prefixes. — The 'no auto-summary' command disables automatic classful summarization in EIGRP. Therefore, EIGRP advertises the exact subnet masks configured under the 'network' statements: 192.168.1.0/24 and 10.0.0.0/8, rather than summarizing them to their classful boundaries (192.168.0.0/16 and 10.0.0.0/8). This ensures that all subnets are advertised with their original prefix lengths.
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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