The correct answer is that EIGRP will form neighbor adjacencies only on GigabitEthernet0/0. This is because the `passive-interface default` command sets every interface on the router to passive mode, which suppresses the sending and receiving of EIGRP hello packets, thereby preventing neighbor formation on all interfaces. The subsequent `no passive-interface GigabitEthernet0/0` command explicitly overrides that default for only that specific interface, allowing it to actively send hellos and establish adjacencies. On the Cisco CCNP ENARSI 300-410 exam, this configuration tests your understanding of the order of operations in EIGRP interface control, where a global default can be selectively reversed. A common trap is assuming that `passive-interface default` blocks all EIGRP activity, but it only blocks neighbor discovery—routes are still advertised from passive interfaces. Remember the mnemonic: "Default blocks the handshake, no passive shakes the one you make."
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.
Consider the following EIGRP configuration on Router R1:
router eigrp 100
network 10.0.0.0
passive-interface default
no passive-interface GigabitEthernet0/0
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
EIGRP will form neighbor adjacencies only on GigabitEthernet0/0.
The configuration sets all interfaces to passive by default, then re-enables EIGRP on GigabitEthernet0/0. This means only GigabitEthernet0/0 will send and receive EIGRP hello packets and form adjacencies; all other interfaces will only advertise networks without forming neighbors.
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 form neighbor adjacencies on all interfaces.
Why it's wrong here
The passive-interface default command prevents neighbor formation on all interfaces unless explicitly removed.
✓
EIGRP will form neighbor adjacencies only on GigabitEthernet0/0.
Why this is correct
The no passive-interface command on GigabitEthernet0/0 allows neighbor formation only on that interface.
GigabitEthernet0/0 is explicitly enabled, so it will form adjacencies.
✗
EIGRP will form neighbor adjacencies on all interfaces except GigabitEthernet0/0.
Why it's wrong here
The no passive-interface command enables neighbor formation on GigabitEthernet0/0, not disables it.
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 passive-interface default command prevents neighbor formation on all interfaces unless explicitly removed.
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 form neighbor adjacencies only on GigabitEthernet0/0. — The configuration sets all interfaces to passive by default, then re-enables EIGRP on GigabitEthernet0/0. This means only GigabitEthernet0/0 will send and receive EIGRP hello packets and form adjacencies; all other interfaces will only advertise networks without forming neighbors.
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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