Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R3# router ospf 1 network 10.20.30.0 0.0.0.255 area 0 network 10.1.23.0 0.0.0.255 area 0 passive-interface GigabitEthernet0/0 interface GigabitEthernet0/0 ip address 10.1.23.3 255.255.255.0
R3 is not receiving the 10.20.30.0/24 network through OSPF. Based on the configuration, what is the most likely cause?
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 passive-interface command is preventing OSPF adjacency on GigabitEthernet0/0.
This is correct because passive-interface stops OSPF hello packets on that interface, which prevents the adjacency needed to exchange routes.
B
Distractor review
OSPF cannot advertise a /24 network with a wildcard mask of 0.0.0.255.
This is wrong because that wildcard mask is normal for matching a /24 network in OSPF network statements.
C
Distractor review
The OSPF process ID must match on every router in the area.
This is wrong because the process ID is locally significant and does not need to match between routers.
D
Distractor review
The router must use a static route before OSPF can advertise the network.
This is wrong because OSPF can advertise directly connected networks without a static route.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that the passive-interface command disables the interface or prevents the network from being advertised in OSPF. In reality, passive-interface only stops OSPF hello packets, so the interface remains up and the network is advertised locally. However, no neighbor adjacency forms on that interface, so no routes are exchanged with neighbors. Candidates often overlook this subtlety and mistakenly blame network statements or process ID mismatches, leading to incorrect troubleshooting conclusions.
Technical deep dive
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that relies on the exchange of hello packets between routers on shared interfaces to establish neighbor adjacencies. These adjacencies are essential for routers to share link-state information and build a consistent routing database. The passive-interface command in OSPF is used to prevent the sending of OSPF hello packets on a specific interface, effectively stopping neighbor discovery on that link while still allowing IP traffic to flow normally. This command is often used to increase security or reduce unnecessary OSPF traffic on interfaces connected to end devices. When a network statement is configured in OSPF, it tells the router which connected interfaces should advertise their networks into the OSPF domain. However, if the interface is marked as passive, the router will advertise the network but will not form neighbor adjacencies on that interface. This means no OSPF hello packets are sent or received, and no routing information is exchanged with neighbors on that link. The OSPF process ID is a local identifier and does not affect adjacency formation, so mismatched process IDs do not cause missing routes. Additionally, OSPF does not require static routes to advertise connected networks; it automatically advertises interfaces included in network statements. The exam trap here is that passive-interface does not disable the interface or its IP connectivity; it only stops OSPF hello packets. This subtlety often confuses candidates who expect that if a network is advertised, routes will be exchanged. In reality, the passive-interface command silently prevents neighbor formation, causing missing routes on adjacent routers. Understanding this behavior is crucial for troubleshooting OSPF connectivity issues and correctly interpreting OSPF configurations in Cisco environments.
KKey Concepts to Remember
- The passive-interface command in OSPF prevents the router from sending OSPF hello packets on the specified interface, which stops neighbor adjacency formation on that link.
- OSPF requires hello packets to be exchanged between routers on an interface to establish neighbor relationships and exchange routing information.
- A network statement in OSPF configures which connected interfaces advertise their networks into the OSPF routing process but does not override passive-interface behavior.
- The OSPF process ID is locally significant and does not need to match between routers for adjacency or route exchange to occur.
- OSPF can advertise directly connected networks without requiring static routes to be configured on the router.
- If an interface is set as passive in OSPF, the router still routes IP traffic on that interface but does not participate in OSPF neighbor discovery or route exchange there.
- Failure to form OSPF adjacency due to passive-interface results in missing routes from neighbors, even if network statements and area configurations are correct.
- Understanding the interaction between OSPF network statements and passive-interface commands is critical to troubleshooting missing OSPF routes in Cisco networks.
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?
The passive-interface command in OSPF prevents the router from sending OSPF hello packets on the specified interface, which stops neighbor adjacency formation on that link.
What is the correct answer to this question?
The correct answer is: The passive-interface command is preventing OSPF adjacency on GigabitEthernet0/0. — The most likely cause is that the passive-interface setting is preventing OSPF hellos from being sent on the link that should form the neighbor relationship. In plain language, the router has been told to advertise the connected network into OSPF but stay quiet on the interface itself. That means the network may appear as a local OSPF statement on the router, but no adjacency forms on that interface, so the route never gets exchanged with the neighboring device. This is a common CCNA trap because passive-interface does not disable the IP address or shut the link down. The interface still works at Layer 3, but OSPF stops sending hello packets there. If the only path for route exchange depends on that interface, the remote router never becomes a neighbor and cannot learn the route. The network statement, area assignment, and process ID may all look fine, but the passive-interface command silently prevents the required OSPF neighbor relationship from forming.
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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