Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# interface GigabitEthernet0/0 ip address 10.1.12.1 255.255.255.0 ip ospf hello-interval 10 ip ospf dead-interval 40 ! router ospf 1 network 10.1.12.0 0.0.0.255 area 0 R2# interface GigabitEthernet0/0 ip address 10.1.12.2 255.255.255.0 ip ospf hello-interval 5 ip ospf dead-interval 20 ! router ospf 20 network 10.1.12.0 0.0.0.255 area 0
Based on the exhibit, what is the most likely reason R1 and R2 are not forming an OSPF adjacency on GigabitEthernet0/0?
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
Distractor review
The OSPF process IDs do not match.
This is wrong because OSPF process IDs are locally significant and do not have to match between neighbors.
B
Best answer
The OSPF hello and dead timers do not match.
This is correct because mismatched OSPF timers prevent adjacency formation.
C
Distractor review
The interfaces are in different IP subnets.
This is wrong because both interfaces are in the 10.1.12.0/24 subnet.
D
Distractor review
The routers must use PPP instead of Ethernet to run OSPF.
This is wrong because OSPF runs normally over Ethernet.
Common exam trap
Common exam trap: answer the scenario, not the keyword
Many candidates mistakenly believe that OSPF process IDs must match between routers to form an adjacency. This is incorrect because OSPF process IDs are locally significant and do not affect neighbor relationships. Focusing on process ID mismatches can waste valuable exam time and distract from the real issue. The actual cause is often mismatched hello and dead timers, which must be identical on both routers to establish adjacency. Overlooking this leads to incorrect conclusions and failure to resolve the adjacency problem.
Technical deep dive
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that establishes neighbor relationships through a process called adjacency formation. OSPF routers exchange hello packets on interfaces to discover and maintain neighbors, requiring several parameters to match exactly, including hello and dead intervals, area ID, subnet, and authentication. These parameters ensure routers trust each other and synchronize their link-state databases for accurate routing. The hello and dead timers are critical OSPF parameters that control how often hello packets are sent and how long a router waits before declaring a neighbor down. Both routers on a shared segment must have matching hello and dead intervals to form an adjacency. If these timers differ, the routers will see each other’s hellos as invalid and never progress beyond the two-way state, preventing full adjacency and routing information exchange. A common exam trap is focusing on OSPF process IDs, which do not need to match because they are locally significant identifiers. Candidates often overlook timer mismatches, which are a frequent cause of adjacency failures in practical networks. Understanding this distinction helps avoid misdiagnosis and ensures proper troubleshooting of OSPF neighbor relationships in Cisco environments.
KKey Concepts to Remember
- OSPF routers must have matching hello and dead timers on interfaces to successfully form neighbor adjacencies.
- OSPF process IDs are locally significant and do not need to match between routers for adjacency formation.
- OSPF adjacency requires interfaces to be in the same IP subnet and area to exchange routing information.
- Mismatched OSPF hello and dead timers prevent routers from progressing beyond the two-way neighbor state.
- OSPF uses hello packets to discover neighbors and dead intervals to determine neighbor failure.
- OSPF adjacency failures often result from interface-level parameter mismatches rather than routing process IDs.
- Cisco routers use 'show ip ospf interface' to verify OSPF timers and interface parameters critical for adjacency.
- Understanding OSPF adjacency requirements helps avoid common exam traps related to process ID and timer confusion.
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 have matching hello and dead timers on interfaces to successfully form neighbor adjacencies.
What is the correct answer to this question?
The correct answer is: The OSPF hello and dead timers do not match. — The most likely reason is that the OSPF hello and dead timers do not match between the two routers. In practical terms, OSPF neighbors on the same segment must agree on several key parameters before they trust one another enough to become adjacent. The IP addressing is in the same subnet and both interfaces are in area 0, so the timer mismatch is the strongest failure point shown. This is a classic OSPF troubleshooting pattern. Many candidates look first for process ID problems, but OSPF process IDs are locally significant and do not need to match between routers.
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.