Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R3 interfaces: G0/0 10.23.23.3/30 G0/1 192.168.50.1/24 router ospf 1 network 10.23.23.0 0.0.0.3 area 0 show ip route on R1: no entry for 192.168.50.0/24
Exhibit: R1 cannot reach 192.168.50.0/24 even though OSPF is running between all routers. Which issue shown is the best explanation?
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
R3 is not advertising the 192.168.50.0/24 LAN into OSPF
Without a matching network statement or interface-level OSPF config, that subnet is not advertised.
B
Distractor review
R1 needs a static default route to learn intra-area OSPF routes
OSPF routes do not require a default route to be learned.
C
Distractor review
The 192.168.50.0/24 network must be converted to a /30
A /24 LAN is normal.
D
Distractor review
The LAN interface on R3 must be shut down for OSPF to advertise it
The opposite is true.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is believing that OSPF automatically advertises all connected interfaces without explicit configuration. Candidates may also incorrectly think that a static default route is necessary for OSPF to learn intra-area routes or that subnet mask changes are required for advertisement. Another misleading idea is that shutting down an interface forces OSPF to advertise it, which is the opposite of correct behavior. These misconceptions can lead to selecting incorrect answers that do not address the root cause of missing route advertisements in OSPF.
Technical deep dive
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that dynamically discovers and advertises routes between routers within an autonomous system. OSPF routers exchange link-state advertisements (LSAs) to build a complete topology map, allowing each router to calculate the shortest path to every network. For a router to advertise a connected subnet in OSPF, the interface must be included in the OSPF process either via a network statement matching the subnet or by enabling OSPF directly on the interface. Without this, the subnet remains unknown to other routers. The decision to advertise a subnet in OSPF depends on proper configuration of network statements or interface OSPF commands. If a router interface connected to a LAN is not included in OSPF, that subnet will not be advertised in LSAs, causing other routers to lack routing information for that network. This leads to connectivity failures, such as R1 being unable to reach 192.168.50.0/24 if R3 does not advertise it. Passive interface settings also affect advertisement, but the primary cause here is the missing network statement for the LAN subnet on R3. A common exam trap is assuming that OSPF automatically advertises all connected subnets or that a static default route is needed to learn intra-area routes. In reality, OSPF requires explicit configuration to advertise each subnet. Also, subnet size (e.g., /24 vs /30) does not impact OSPF advertisement eligibility. Understanding these nuances prevents misdiagnosis of routing issues and ensures correct OSPF operation in Cisco networks.
KKey Concepts to Remember
- OSPF advertises connected subnets only if the interface is included in the OSPF process via network statements or interface configuration.
- A missing network statement on a router prevents that router from advertising the connected subnet into the OSPF domain.
- OSPF routers exchange link-state advertisements to build a topology map and calculate shortest paths to all known networks.
- Passive interfaces in OSPF do not send or receive routing updates, which can prevent subnet advertisement if misconfigured.
- OSPF does not require static default routes to learn intra-area routes because it dynamically shares routing information.
- Subnet mask size does not affect whether OSPF advertises a subnet; a /24 is a valid subnet for OSPF advertisement.
- Shutting down an interface disables it and prevents OSPF from advertising the connected subnet, the opposite of enabling advertisement.
- Proper OSPF configuration ensures all routers have consistent routing tables and reachability to all advertised subnets.
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?
OSPF advertises connected subnets only if the interface is included in the OSPF process via network statements or interface configuration.
What is the correct answer to this question?
The correct answer is: R3 is not advertising the 192.168.50.0/24 LAN into OSPF — If an interface connected to the destination subnet is configured as passive or active in OSPF incorrectly? Wait. Here the real clue is that the destination LAN network statement is missing from R3, so OSPF never advertises 192.168.50.0/24 to the rest of the domain.
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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