Question 1mediummulti select
Full question →mediummulti selectObjective-mapped
Which two statements about OSPF neighbor requirements on a shared Ethernet segment are correct? (Choose two.)
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
They must be in the same OSPF area on that link.
Correct. Area mismatch prevents adjacency.
B
Best answer
They must use the same subnet on the connected interfaces.
Correct. OSPF neighbors on a shared segment must be directly reachable at Layer 3.
C
Distractor review
They must have identical router IDs.
Router IDs must be unique, not identical.
D
Distractor review
They must use the same process ID number on both routers.
The process ID is locally significant only.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is confusing the OSPF process ID with the area ID or router ID requirements. Candidates often think the process ID must match between neighbors, but it is locally significant and does not affect adjacency. Another common mistake is assuming router IDs must be identical; in fact, router IDs must be unique within the OSPF domain to prevent routing conflicts. Misunderstanding these distinctions can lead to selecting incorrect answers about neighbor requirements. The key is to focus on area ID and subnet matching for adjacency on shared Ethernet segments, not process ID or identical router IDs.
Technical deep dive
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that forms neighbor adjacencies to exchange routing information. On a shared Ethernet segment, OSPF routers send multicast Hello packets to discover neighbors and establish adjacencies. These Hello packets contain critical information such as the router's OSPF area ID, subnet, Hello and Dead intervals, and router ID. For two routers to become OSPF neighbors on a shared Ethernet link, they must be in the same OSPF area and use the same subnet on their connected interfaces. This ensures that the routers are logically connected within the same routing domain and can communicate directly at Layer 3. The requirement for matching OSPF area IDs on a shared segment is fundamental because OSPF organizes routers into areas to optimize routing and reduce overhead. Routers in different areas do not form neighbor relationships on the same link. Similarly, the subnet on the connected interfaces must be identical so that the routers can reach each other directly via IP. Without the same subnet, Hello packets will not be received or acknowledged, preventing adjacency formation. The OSPF process ID, however, is locally significant and does not need to match between neighbors, while router IDs must be unique to avoid routing conflicts. A common exam trap is confusing the OSPF process ID and router ID requirements. Many candidates mistakenly believe that the process ID must match between neighbors, but it only identifies the OSPF instance locally on a router. Another trap is assuming router IDs must be identical; in reality, they must be unique. Understanding these distinctions helps avoid incorrect answers. In practical networks, ensuring area and subnet consistency on shared Ethernet segments is critical for OSPF neighbor relationships and stable routing operation.
KKey Concepts to Remember
- OSPF routers must be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information.
- OSPF neighbors on a shared Ethernet link must use the same subnet on their connected interfaces to ensure Layer 3 reachability and successful Hello packet exchange.
- OSPF router IDs must be unique within the OSPF domain to prevent routing conflicts but do not need to be identical between neighbors.
- The OSPF process ID is locally significant to each router and does not affect neighbor relationships or adjacency formation.
- OSPF Hello packets include the area ID and subnet information, which neighbors use to verify compatibility before forming adjacencies.
- Mismatch in OSPF area ID or subnet between routers on the same Ethernet segment prevents neighbor adjacency and routing updates.
- OSPF uses multicast Hello packets on shared Ethernet segments to discover neighbors and establish adjacencies based on matching parameters.
- OSPF adjacency formation on shared media requires agreement on key parameters such as area ID, subnet, Hello and Dead intervals.
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 be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information.
What is the correct answer to this question?
The correct answer is: They must be in the same OSPF area on that link. — Neighbors must agree on key parameters such as area ID and subnet, and they exchange Hello packets on the segment.
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.