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.”
300-410 EIGRP Troubleshooting Practice Question
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?
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 summarization at classful boundaries, so EIGRP will advertise subnets exactly as configured under the network statements.
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.
✗
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.
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: 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.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — OSPF neighbours must agree on key parameters..
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 summarization at classful boundaries, so EIGRP will advertise subnets exactly as configured under the network statements.
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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