OSPFv2 Single-Area Fundamentals: Adjacency and Area 0 Basics

Free preview — the first lab of OSPF: Adjacency to Multi-Area Mastery

Hands-on CCNA beginner lab: build a 3-router chain with end hosts, enable OSPFv2 area 0, form full adjacencies, advertise loopbacks and LANs, verify route propagation end-to-end, and intentionally create then resolve an OSPF area mismatch on a transit segment.

Learning objectives

• Enable OSPFv2 process 1 on all routers with a stable router-id sourced from Loopback0.
• Advertise loopbacks and all connected LAN/transit networks in area 0 using correct wildcard masks.
• Suppress OSPF hellos on all interfaces by default, then re-enable them only on the router-to-router transit links.
• Verify neighbor adjacency states, LSDB sync, and route propagation across the chain.
• Reproduce an OSPF area mismatch on a transit link, analyze symptoms, and correct the configuration.

Troubleshooting focus

• If neighbors don’t form: Check interface status and IP/mask on both ends of the transit; errors here block OSPF entirely.; Compare areas on both sides of the link (show ip ospf interface brief). Mismatched areas prevent adjacency.; Ensure the transit interface is not passive; passive blocks hellos.; Confirm MTU/timers/defaults; mismatches can stall in EXSTART/EXCHANGE. Use defaults for this lab.
• If routes don’t appear: Verify loopbacks and LANs are covered by OSPF network statements.; Confirm neighbor state is FULL; no FULL, no LSDB sync.
• If host pings fail: Verify the default gateways on the hosts and the presence of OSPF routes on each router for the remote LAN.; Use traceroute from the host to find the hop where traffic stops.

Topology