350-501 Architecture Practice Question
A network engineer is troubleshooting an OSPF issue in a service provider network. The network uses OSPFv2 with multiple areas. Routers in area 0 are able to ping each other, but routers in area 1 cannot reach routers in area 2. All routers are OSPF-enabled and have correct network type configurations. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the misconception that OSPF areas can communicate directly without the backbone, leading candidates to overlook the mandatory role of ABRs and area 0 in inter-area routing.
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
✓
Missing or misconfigured ABRs between area 1 and area 0, or area 2 and area 0
In OSPFv2, inter-area communication must traverse area 0 (the backbone). Routers in area 1 and area 2 can only reach each other if Area Border Routers (ABRs) exist between each non-backbone area and area 0, and those ABRs are correctly configured and have full adjacencies. Since area 0 routers can ping each other but area 1 and area 2 cannot, the most likely cause is a missing or misconfigured ABR on either side, preventing the exchange of Type 3 summary LSAs between the areas.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Missing or misconfigured ABRs between area 1 and area 0, or area 2 and area 0
Why this is correct
Inter-area routing must go through area 0; without proper ABRs, areas cannot exchange routes.
- ✗
Mismatched OSPF area IDs on routers in area 1 and area 2
Why it's wrong here
Area IDs are local and do not need to match across areas.
- ✗
Lack of BGP peering between ABRs
Why it's wrong here
BGP is not required for OSPF inter-area routing.
- ✗
OSPF network type mismatch preventing adjacency formation
Why it's wrong here
The question states correct network type configurations, so this is not the issue.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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