CCNA 200-301 v1.1 reference — IP Connectivity
OSPF adjacency troubleshooting
Evidence-led OSPF diagnosis: neighbor states, mismatched parameters and passive interfaces, separating symptoms from confirmed causes.
Objective 3.4v1.1 exam target
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Neighbor states and what they mean
| State | Meaning | If stuck here, suspect |
|---|---|---|
| DOWN | No hellos received | Link down, OSPF not enabled, passive, ACL blocking protocol 89 |
| INIT | Hello received, own RID not yet seen | One-way reachability, multicast filtering |
| 2-WAY | Bidirectional — DR election point | Normal on broadcast between DROTHERs; if stuck FULL needed, check network types |
| EXSTART | Master/slave DBD negotiation | MTU mismatch is the classic cause |
| EXCHANGE | DBD packets flowing | MTU or duplicate RID |
| LOADING | Requesting LSAs | LSA corruption/flood issues |
| FULL | Databases synchronized | The goal — adjacency complete |
Mismatch → where to look
| Requirement | Verification command |
|---|---|
| Same area | show ip ospf interface brief — the area column |
| Same subnet | show ip interface on both ends |
| Hello/dead match | show ip ospf interface — timer line |
| MTU match | show interfaces — MTU field both ends |
| Auth match | show ip ospf interface — auth type line |
| Unique RID | show ip ospf — the router ID field |
| Not passive | show ip protocols — passive interface list |
| Protocol 89 allowed | Interface ACLs + debug ip ospf hello |
Verification toolbox
show ip ospf neighbor— state and role per neighbor.show ip ospf interface— network type, timers, cost, passive.show ip ospf database— the LSDB itself.show ip route ospf— what OSPF actually installed.debug ip ospf adj/hello— the mismatch in the device's own words (lab only).
Related resources
Sources
- Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
- RFC 2328 — OSPF Version 2 — reviewed 2026-11-02
- Cisco — IP Routing: OSPF Command Reference — reviewed 2026-11-02
Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.