Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# interface GigabitEthernet0/0 ip address 10.1.50.1 255.255.255.0 ! router ospf 1 network 10.1.50.0 0.0.0.255 area 0 R2# interface GigabitEthernet0/0 ip address 10.1.50.2 255.255.255.0 ! router ospf 1 network 10.1.50.0 0.0.0.255 area 1
Based on the exhibit, what is the most likely reason R1 is not forming an OSPF adjacency with R2?
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 OSPF areas do not match on the shared segment.
This is correct because the same link is placed into area 0 on one side and area 1 on the other.
B
Distractor review
The routers must use different process IDs.
This is wrong because matching or differing local process IDs is not the issue here.
C
Distractor review
The interfaces are in different IPv4 subnets.
This is wrong because both are in 10.1.50.0/24.
D
Distractor review
OSPF cannot run on Ethernet interfaces.
This is wrong because OSPF commonly runs on Ethernet.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that OSPF process IDs must match on both routers to form adjacency. Many candidates mistakenly believe that differing process IDs prevent neighbor relationships, but process IDs are local to each router and do not need to match. Another common mistake is focusing on IP subnet mismatches or interface types, which are often correct but not the root cause here. The real issue is the OSPF area mismatch, which is less obvious but critical. Ignoring the area ID difference leads to confusion because routers can be on the same subnet and exchange hellos but never form adjacency.
Technical deep dive
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that forms neighbor adjacencies between routers on shared network segments. For two routers to establish an OSPF adjacency, they must agree on several parameters, including the subnet, hello and dead intervals, authentication, and crucially, the OSPF area assigned to the interface. The OSPF area is a logical grouping that segments the network to optimize routing and reduce overhead. Routers on the same physical segment must place that interface in the same OSPF area to exchange link-state advertisements and form a neighbor relationship. The OSPF adjacency formation process involves routers exchanging hello packets to discover neighbors and negotiate parameters. If the routers detect a mismatch in the OSPF area ID on their connected interfaces, they will not progress beyond the initial hello exchange, preventing adjacency formation. This area mismatch acts as a fundamental barrier because OSPF treats each area as a separate routing domain, and adjacency is only valid within the same area. Cisco IOS requires exact area ID matches on both ends of a link for adjacency to form. A common exam trap is to overlook the OSPF area mismatch and instead focus on other parameters like process IDs or IP subnet mismatches. While process IDs are locally significant and can differ without affecting adjacency, the area ID must match exactly. In practical network troubleshooting, an area mismatch can cause silent failures where routers appear connected at Layer 2 and share IP subnets but never become OSPF neighbors. Recognizing this subtle but critical configuration error is essential for both exam success and real-world OSPF troubleshooting.
KKey Concepts to Remember
- OSPF routers must assign the same area ID to interfaces on a shared segment to form neighbor adjacencies successfully.
- OSPF process IDs are local to each router and do not need to match for adjacency to form between neighbors.
- OSPF adjacency formation requires matching hello and dead intervals, subnet, authentication, and area ID on connected interfaces.
- Routers on the same IP subnet but with different OSPF area assignments will not establish an OSPF neighbor relationship.
- An OSPF area mismatch prevents the exchange of link-state advertisements, blocking routing updates between neighbors.
- OSPF adjacency failures due to area mismatches often appear as silent failures with no neighbor state progression beyond 'Init' or '2-Way'.
- Correct OSPF configuration requires consistent area assignment on both ends of a link to ensure proper routing domain segmentation.
- Exam candidates should prioritize verifying OSPF area consistency before troubleshooting other parameters like process ID or interface type.
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
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 routers must assign the same area ID to interfaces on a shared segment to form neighbor adjacencies successfully.
What is the correct answer to this question?
The correct answer is: The OSPF areas do not match on the shared segment. — The most likely reason is an OSPF area mismatch on the connected interfaces. In practical terms, the routers are on the same IP subnet, and the hello timers shown are not the issue, but each side places the shared link into a different OSPF area. OSPF neighbors on the same segment must agree on the area for the adjacency to form. This is a classic OSPF troubleshooting item because everything can look almost correct at first glance. One incorrect area value is enough to block the neighbor relationship.
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.
Discussion
Loading comments…
Sign in to join the discussion.