Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Why does a passive interface in OSPF still matter even though it does not send hello packets?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The connected network can still be advertised into OSPF through other active adjacencies
This is correct because passive-interface suppresses hello exchange on that interface while still allowing the network to be advertised.
B
Distractor review
The passive interface automatically becomes the OSPF router ID
This is wrong because passive-interface status does not determine the router ID.
C
Distractor review
The passive interface disables all OSPF operation on the router
This is wrong because OSPF can still run and form adjacencies on other interfaces.
D
Distractor review
The passive interface converts OSPF into EIGRP on that link
This is wrong because passive-interface affects OSPF hello behavior only.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is misunderstanding the passive interface’s role and assuming it disables all OSPF activity on that interface, including network advertisement. Many candidates incorrectly believe that passive means the network is ignored or not advertised, leading to wrong answers. In reality, passive interfaces stop hello packets and neighbor formation but still advertise the connected network in OSPF LSAs. This subtlety is crucial because the router continues to inform other OSPF routers about the network, just without forming adjacencies on the passive interface itself. Confusing passive with a complete OSPF shutdown on the interface causes errors in both exam and real-world scenarios.
Technical deep dive
How to think about this question
In OSPF (Open Shortest Path First), a passive interface is configured to stop sending OSPF hello packets on that interface, which prevents the formation of OSPF neighbor adjacencies over that link. However, the interface’s connected network is still advertised into the OSPF routing domain. This means the router informs other OSPF routers about the network reachable via the passive interface without actively participating in OSPF neighbor discovery or adjacency formation on that link. The decision to configure an interface as passive is based on the need to advertise the connected network while avoiding unnecessary OSPF overhead or security risks on interfaces where no OSPF neighbors should exist, such as user-facing LAN ports or stub networks. The router continues to include the passive interface’s network in its Link State Advertisements (LSAs), allowing other routers to learn about the network without requiring OSPF hello exchanges or adjacency formation on that interface. A common exam trap is assuming that passive interface means the network is not advertised or that OSPF is disabled entirely on that interface. In reality, passive interfaces still advertise their connected networks but do not form neighbor relationships. This distinction is critical for network design and security, as it allows controlled advertisement without exposing OSPF to unnecessary or untrusted neighbors. Practically, passive interfaces reduce OSPF traffic and prevent unwanted neighbor adjacencies while maintaining accurate routing information.
KKey Concepts to Remember
- A passive interface in OSPF prevents sending hello packets and forming neighbor adjacencies on that interface while still advertising the connected network.
- OSPF routers advertise networks on passive interfaces through Link State Advertisements even though no OSPF neighbor is formed on those interfaces.
- Configuring an interface as passive is useful on user-facing or stub interfaces where OSPF neighbor relationships are unnecessary or undesirable.
- Passive interfaces reduce OSPF protocol overhead by stopping hello packet exchanges without disabling OSPF routing on the router.
- The passive interface setting does not affect the router ID or OSPF operation on other active interfaces.
- OSPF continues to run normally on other interfaces, forming adjacencies and exchanging routing information despite passive interfaces.
- A common mistake is to assume passive means the network is not advertised, but OSPF still advertises the network to other routers.
- Passive interfaces enhance network security by preventing OSPF neighbor formation on interfaces connected to untrusted or end-user devices.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A passive interface in OSPF prevents sending hello packets and forming neighbor adjacencies on that interface while still advertising the connected network.
What is the correct answer to this question?
The correct answer is: The connected network can still be advertised into OSPF through other active adjacencies — A passive interface still matters because the connected network can still be advertised into OSPF even though the interface itself does not form neighbor relationships. In plain language, the router is saying, “This network is mine, and I want others to know about it, but I do not want to speak OSPF directly on this interface.” That is useful on user-facing or stub-like interfaces where no OSPF neighbor should exist. This distinction is important because some engineers assume passive means “ignored entirely.” It does not. The connected network can still appear in routing updates sent through real neighbors on other interfaces. What changes is neighbor formation on the passive interface itself.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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