Break-fix: OSPF area mismatch

Troubleshooting
Intermediate
10 min
4 steps
Cisco IOS-style

Three routers run OSPF. One LAN is unreachable because a router has an interface in the wrong area. Diagnose and fix it.

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Free · no install · no account

Scenario

OSPF only forms adjacencies between neighbors in the same area on the same physical link. An area mismatch silently prevents adjacency formation — show ip ospf neighbor simply doesn't list the neighbor at all.

Topology

3 × router · Cisco IOS-style

R1 — router
R2 — router
R3 — router

What you will do

Confirm the symptom first: from R1, ping R3's loopback (192.168.3.1). Should fail.
On R2 run show ip ospf neighbor — does R1 show up?
On R2, change the network statement for 10.0.0.0/30 to area 0.
Ping 192.168.3.1 from R1 again — should now succeed.

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Break-fix: OSPF area mismatch

Scenario

Topology

What you will do

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