The answer is that only GigabitEthernet0/0 is active, while all other OSPF interfaces become passive. This is correct because the `passive-interface default` command globally suppresses OSPF hello packets on every interface, preventing neighbor discovery and adjacency formation. The subsequent `no passive-interface GigabitEthernet0/0` explicitly overrides that default for that single interface, restoring its ability to send and receive hellos. On the ENCOR 350-401 exam, this configuration tests your understanding of how OSPF interface states are managed hierarchically—a common trap is assuming `passive-interface default` blocks routing updates entirely, when in fact it only stops hello exchange; routes learned via other means are still advertised. A solid memory tip: think of it as a “deny all, permit one” ACL for OSPF hellos—the default command locks every door, and the `no passive-interface` command unlocks only the specified door.
CCNP OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Router R6 has the following OSPF configuration:
router ospf 1
router-id 6.6.6.6
network 192.168.0.0 0.0.255.255 area 0
passive-interface default
no passive-interface GigabitEthernet0/0
!
interface GigabitEthernet0/0
ip address 192.168.1.6 255.255.255.0
ip ospf 1 area 0
What is the effect of the 'passive-interface default' command?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Only GigabitEthernet0/0 is active; all other OSPF interfaces are passive.
The 'passive-interface default' command sets all OSPF interfaces to passive by default, meaning they will not send or receive OSPF hello packets and thus cannot form adjacencies. The subsequent 'no passive-interface GigabitEthernet0/0' overrides this for that specific interface, making it the only active OSPF interface. This matches option B.
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.
✗
All OSPF interfaces become passive, including GigabitEthernet0/0.
Why it's wrong here
The 'no passive-interface' command for GigabitEthernet0/0 overrides the default, making it active.
✓
Only GigabitEthernet0/0 is active; all other OSPF interfaces are passive.
Why this is correct
The default passive setting applies to all interfaces except those explicitly set to 'no passive-interface'.
Related concept
Read the scenario before looking for a memorised answer.
✗
OSPF adjacencies are formed on all interfaces.
Why it's wrong here
Passive interfaces do not form adjacencies; only the non-passive interface does.
✗
The 'passive-interface default' command is ignored because the 'network' command is used.
Why it's wrong here
The 'passive-interface default' command is valid and takes effect regardless of the network command.
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' to see if candidates understand that the default command applies to all interfaces and must be explicitly overridden per interface, rather than assuming the 'network' command alone controls adjacency formation.
Trap categories for this question
Command / output trap
The 'no passive-interface' command for GigabitEthernet0/0 overrides the default, making it active.
Detailed technical explanation
How to think about this question
The 'passive-interface default' command is often used in hub-and-spoke topologies or when connecting to stub networks to prevent unnecessary OSPF hello traffic and neighbor state maintenance. Under the hood, a passive interface still advertises its connected subnet as a stub network (type 3 LSA) but does not send or process hello packets, so no neighbor relationship is established. This is particularly useful on loopback interfaces or LAN segments where you want to advertise the subnet without forming adjacencies.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
OSPF — This question tests OSPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Only GigabitEthernet0/0 is active; all other OSPF interfaces are passive. — The 'passive-interface default' command sets all OSPF interfaces to passive by default, meaning they will not send or receive OSPF hello packets and thus cannot form adjacencies. The subsequent 'no passive-interface GigabitEthernet0/0' overrides this for that specific interface, making it the only active OSPF interface. This matches option B.
What should I do if I get this 350-401 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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