# OSPF: Neighbor 10.0.0.2 stuck in EXSTART state

- **ID:** `networking/ospf-neighbor-stuck-in-exstart`
- **Domain:** networking
- **Category:** network_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

OSPF neighbors are unable to exchange Database Description (DBD) packets due to MTU mismatch, interface duplex mismatch, or OSPF network type misconfiguration, preventing the adjacency from progressing beyond the EXSTART phase.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| Cisco IOS 15.7 | active | — | — |
| FRRouting 8.4 | active | — | — |
| Quagga 1.2.4 | active | — | — |

## Workarounds

1. **Verify and set the same MTU on both interfaces: `ip mtu 1500` on both ends, or enable IP fragmentation for OSPF with `ip ospf mtu-ignore`.** (90% success)
   ```
   Verify and set the same MTU on both interfaces: `ip mtu 1500` on both ends, or enable IP fragmentation for OSPF with `ip ospf mtu-ignore`.
   ```
2. **Ensure both interfaces have the same OSPF network type: `ip ospf network point-to-point` on both sides (common fix for frame relay or Ethernet).** (85% success)
   ```
   Ensure both interfaces have the same OSPF network type: `ip ospf network point-to-point` on both sides (common fix for frame relay or Ethernet).
   ```
3. **Check for duplex mismatch: use `show interfaces` to confirm both are full duplex; set with `duplex full` if needed.** (80% success)
   ```
   Check for duplex mismatch: use `show interfaces` to confirm both are full duplex; set with `duplex full` if needed.
   ```

## Dead Ends

- **** — This restarts the adjacency but the same issue will reoccur because the root cause (e.g., MTU mismatch) is not addressed. (90% fail)
- **** — The EXSTART state is not timer-dependent; it is a protocol handshake issue. Changing timers only delays the failure. (70% fail)
- **** — Router ID does not affect the DBD exchange process; the adjacency will still get stuck in EXSTART. (85% fail)