networking network_error ai_generated true

OSPF: Neighbor 10.0.0.2 stuck in EXSTART state

ID: networking/ospf-neighbor-stuck-in-exstart

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
1Evidence
2024-01-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
Cisco IOS 15.7 active — — —
FRRouting 8.4 active — — —
Quagga 1.2.4 active — — —

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.

generic

中文

OSPF邻居无法交换数据库描述（DBD）数据包，原因包括MTU不匹配、接口双工模式不匹配或OSPF网络类型配置错误，导致邻接关系无法从EXSTART阶段继续。

Official Documentation

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13684-12.html

Workarounds

  1. 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`. 
    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. 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). 
    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. 80% success Check for duplex mismatch: use `show interfaces` to confirm both are full duplex; set with `duplex full` if needed. 
    Check for duplex mismatch: use `show interfaces` to confirm both are full duplex; set with `duplex full` if needed.

中文步骤

  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`.
  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).
  3. Check for duplex mismatch: use `show interfaces` to confirm both are full duplex; set with `duplex full` if needed.

Dead Ends

Common approaches that don't work:

  1. 90% fail

    This restarts the adjacency but the same issue will reoccur because the root cause (e.g., MTU mismatch) is not addressed.

  2. 70% fail

    The EXSTART state is not timer-dependent; it is a protocol handshake issue. Changing timers only delays the failure.

  3. 85% fail

    Router ID does not affect the DBD exchange process; the adjacency will still get stuck in EXSTART.