CCNA IP Routing Practice Question
Which two statements accurately describe OSPF passive interfaces?
⚠ Common exam trap
A common exam trap is to confuse the effect of the OSPF passive interface command with disabling OSPF entirely on that interface or converting OSPF routes into static routes. Some candidates mistakenly believe that passive interfaces stop all OSPF activity or remove the network from OSPF advertisements. In reality, passive interfaces only stop OSPF hello packets and adjacency formation but continue to advertise the connected network. Misunderstanding this can lead to incorrect answers or network misconfigurations, especially when interpreting how OSPF maintains routing information despite passive interfaces.
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
✓
It prevents OSPF from sending hello packets on that interface.
An OSPF passive interface stops hello packet exchange on that interface while still allowing the connected network to be advertised into OSPF through other active adjacencies. In plain language, it tells the router not to try to form neighbors on that interface, but not to forget that the network exists. This is very useful on user-facing or stub-like interfaces where no routing neighbor should appear. The wrong answers often treat passive as if it disables OSPF globally or removes the network completely. The two correct answers are the ones that preserve the suppression of adjacency on that interface and the continued advertisement of the connected network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It prevents OSPF from sending hello packets on that interface.
Why this is correct
The OSPF passive-interface command suppresses the transmission of hello packets out of that specific interface, preventing the router from establishing or maintaining neighbor adjacencies on that link. Because OSPF relies on hello packets over multicast 224.0.0.5 to discover neighbors, a passive interface will not send or receive those hellos, so no OSPF neighbor relationship can form there. However, the interface remains an OSPF-attached network and its prefix is still injected into the LSDB and advertised to other neighbors reachable through active interfaces.
- ✓
It can still allow the connected network to be advertised into OSPF.
Why this is correct
Even when an interface is made passive, OSPF does not remove that interface's connected subnet from the routing process or from the router's link-state advertisements. The passive-interface command only stops hello and adjacency formation locally; the prefix continues to be advertised into OSPF as a stub network through the router's normal LSA generation, and other routers learn it via active OSPF-speaking links. Thus, reachability to the passive network remains available to the rest of the OSPF domain.
- ✗
It changes OSPF into a static route on that interface.
Why it's wrong here
Passive-interface does not alter the underlying routing protocol or convert OSPF into a static route, nor does it install any static entry in the RIB. OSPF remains a fully dynamic protocol, and the prefix associated with the passive interface is still learned and propagated through OSPF's SPF calculations. The command only modifies the interface's behavior with respect to hello packet exchange.
When this WOULD be correct
In a different question asking about the effects of configuring OSPF on a specific interface, if the question stated that passive interfaces behave like static routes in terms of not participating in OSPF neighbor relationships, option C could be considered correct.
- ✗
It forces the interface to become the router ID.
Why it's wrong here
Router ID selection in OSPF is based on the highest IPv4 address among loopback interfaces, or if none are loopback, among active physical interfaces, and can be manually overridden with the router-id command. The passive-interface command has no direct relationship to this election process; it neither forces nor prevents an interface from becoming the router ID. Any correlation is coincidental and depends on IP addressing, not on the interface's passive state.
When this WOULD be correct
In a question asking about OSPF configuration where the context is about defining router roles or attributes, one might state that a specific interface is being used to define the router ID, making it the correct answer in that scenario.
- ✗
It disables OSPF on every interface in the router automatically.
Why it's wrong here
By default, the passive-interface command only affects the single interface named in the command, leaving all other OSPF-enabled interfaces fully operational to send hellos and form adjacencies. To disable OSPF hello processing on all interfaces simultaneously, you would need to issue a broader command such as 'passive-interface default' and then re-enable individual interfaces with 'no passive-interface'. The default behavior is interface-specific, not router-wide.
When this WOULD be correct
In a different question, if it asked about a command that globally disables OSPF on all interfaces when applied, then 'disables OSPF on every interface in the router automatically' could be correct in the context of a command that applies to all interfaces, such as 'router ospf 1' with a specific configuration.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓It prevents OSPF from sending hello packets on that interface.Correct answer▾
Why this is correct
The OSPF passive-interface command suppresses the transmission of hello packets out of that specific interface, preventing the router from establishing or maintaining neighbor adjacencies on that link. Because OSPF relies on hello packets over multicast 224.0.0.5 to discover neighbors, a passive interface will not send or receive those hellos, so no OSPF neighbor relationship can form there. However, the interface remains an OSPF-attached network and its prefix is still injected into the LSDB and advertised to other neighbors reachable through active interfaces.
✗It changes OSPF into a static route on that interface.Wrong answer — click to see why▾
Why this is wrong here
The passive-interface command does not convert OSPF to static routing. OSPF remains a dynamic routing protocol; the interface simply stops sending and receiving OSPF hello packets. The network is still advertised via OSPF if configured appropriately.
★ When this WOULD be the correct answer
In a different question asking about the effects of configuring OSPF on a specific interface, if the question stated that passive interfaces behave like static routes in terms of not participating in OSPF neighbor relationships, option C could be considered correct.
Why candidates choose this
The term 'passive' might be misinterpreted as making the route static or non-dynamic. Students may think that a passive interface means the route becomes static, but in OSPF, passive only suppresses hello packets, not the dynamic advertisement of the network.
✗It forces the interface to become the router ID.Wrong answer — click to see why▾
Why this is wrong here
The passive-interface command does not influence the router ID selection. The router ID is determined by the highest loopback IP address, then the highest physical IP address, or manually configured with the router-id command. Passive-interface only affects OSPF operation on that interface.
★ When this WOULD be the correct answer
In a question asking about OSPF configuration where the context is about defining router roles or attributes, one might state that a specific interface is being used to define the router ID, making it the correct answer in that scenario.
Why candidates choose this
Students might confuse the passive-interface command with other OSPF configuration commands that affect router identity, such as router-id, or mistakenly think that making an interface passive somehow promotes it to a special role like the router ID.
✗It disables OSPF on every interface in the router automatically.Wrong answer — click to see why▾
Why this is wrong here
By default, the passive-interface command applies only to the specified interface. To make all interfaces passive by default, the passive-interface default command must be used, followed by no passive-interface on specific interfaces where adjacencies are desired.
★ When this WOULD be the correct answer
In a different question, if it asked about a command that globally disables OSPF on all interfaces when applied, then 'disables OSPF on every interface in the router automatically' could be correct in the context of a command that applies to all interfaces, such as 'router ospf 1' with a specific configuration.
Why candidates choose this
The word 'passive' might imply a global effect, and students may assume that configuring passive-interface on one interface disables OSPF on all interfaces. However, OSPF passive interfaces are interface-specific unless the default keyword is used.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
Packet
A packet is a small unit of data that is sent over a network, containing both the actual data and control information for delivery.
Key term
Passive interface
A passive interface is a network interface that participates in a routing protocol (like OSPF) by listening for and learning routes, but does not send routing protocol messages out of that interface.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.