- A
EIGRP will form neighbor adjacencies on all interfaces.
Why wrong: The passive-interface default command prevents neighbor formation on all interfaces unless explicitly removed.
- B
EIGRP will form neighbor adjacencies only on GigabitEthernet0/0.
The no passive-interface command on GigabitEthernet0/0 allows neighbor formation only on that interface.
- C
EIGRP will not form any neighbor adjacencies.
Why wrong: GigabitEthernet0/0 is explicitly enabled, so it will form adjacencies.
- D
EIGRP will form neighbor adjacencies on all interfaces except GigabitEthernet0/0.
Why wrong: The no passive-interface command enables neighbor formation on GigabitEthernet0/0, not disables it.
Question 27 of 2,152
EIGRP Passive-Interface Default: How It Works
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
What is the effect of this configuration?
Quick Answer
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."
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 form neighbor adjacencies only on GigabitEthernet0/0.
The 'passive-interface default' command sets all interfaces to passive by default, preventing EIGRP from sending or receiving hello packets on them. The 'no passive-interface GigabitEthernet0/0' command then overrides this default for that specific interface, allowing EIGRP to send and receive hellos and thus form neighbor adjacencies only on GigabitEthernet0/0.
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 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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
EIGRP will not form any neighbor adjacencies.
Why it's wrong here
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: answer the scenario, not the keyword
Cisco often tests the interaction between 'passive-interface default' and 'no passive-interface', where candidates mistakenly think the default command blocks all adjacencies permanently or confuse which interfaces are enabled versus disabled.
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
When EIGRP is configured with 'passive-interface default', all interfaces are placed in passive mode, meaning they do not send EIGRP hello packets and ignore received hellos, effectively preventing neighbor discovery. The 'no passive-interface' command selectively removes this restriction on a per-interface basis, allowing EIGRP to operate normally on that interface. This is commonly used in hub-and-spoke topologies where only specific interfaces should form adjacencies, or to reduce unnecessary EIGRP traffic on LAN segments.
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.
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 form neighbor adjacencies only on GigabitEthernet0/0. — The 'passive-interface default' command sets all interfaces to passive by default, preventing EIGRP from sending or receiving hello packets on them. The 'no passive-interface GigabitEthernet0/0' command then overrides this default for that specific interface, allowing EIGRP to send and receive hellos and thus form neighbor adjacencies only on GigabitEthernet0/0.
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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