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300-410 Practice Question: Two routers R1 and R2 are connected via a…
Two routers R1 and R2 are connected via a FastEthernet link. OSPF is configured on both with network type broadcast. R1 shows: 'show ip ospf neighbor' lists R2 as FULL/DR. R2 shows: 'show ip ospf neighbor' lists R1 as FULL/BDR. However, pings between loopback interfaces on R1 and R2 fail intermittently. 'show ip route' on R1 shows the loopback of R2 as reachable via OSPF, but 'show ip ospf interface' on R1 shows the link as point-to-point. What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that a FULL neighbor state guarantees correct OSPF operation, but here the mismatch in network type causes subtle forwarding issues even though the adjacency appears established.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
One router has 'ip ospf network point-to-point' configured, while the other uses the default broadcast, causing a mismatch in the network type.
The root cause is a mismatch in OSPF network type between R1 and R2. R1's 'show ip ospf interface' shows the link as point-to-point, indicating that 'ip ospf network point-to-point' is configured on R1, while R2 uses the default broadcast type. This mismatch causes R1 to not send OSPF hello packets with the correct multicast address (224.0.0.5 for point-to-point vs. 224.0.0.6 for broadcast DR/BDR election), leading to intermittent connectivity and the observed neighbor states (FULL/DR and FULL/BDR) that appear correct but are actually unstable.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
One router has 'ip ospf network point-to-point' configured, while the other uses the default broadcast, causing a mismatch in the network type.
Why this is correct
A network type mismatch prevents proper OSPF operation; broadcast expects DR/BDR election, while point-to-point does not, leading to inconsistent neighbor states and potential forwarding issues.
- ✗
The FastEthernet interface is operating at half-duplex, causing packet loss.
Why it's wrong here
Duplex mismatch could cause issues, but the OSPF neighbor state would not show FULL/DR if that were the case.
- ✗
OSPF hello and dead timers are mismatched, preventing adjacency formation.
Why it's wrong here
The neighbor state is FULL, so timers are consistent.
- ✗
The MTU on the link is mismatched, causing OSPF packets to be dropped.
Why it's wrong here
MTU mismatch typically prevents adjacency from forming, but here it is FULL.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.