← Problem Library
Network L5 NETWORK-1491 · 11 min

An OSPF adjacency reaches ExStart and resets because the firewall cluster rewrites the MTU on one failover member only

The routing config matches, but one active member injects a different effective MTU after takeover.

NetworkFoundation OpsLevel 5Free11 min
Scenario

An OSPF adjacency flaps only after failover on a firewall cluster sitting between routers.

What to check first
  • Identify the primary failure signal in the The Neighbors Agreed to Talk and the Standby Member Put a Different Size Envelope on the Conversation When It Took Over scenario.
  • Separate visible symptoms from the underlying technical dependency.
  • Describe the safest recovery path and the follow-up prevention work.
Checking checklist
  1. Summarize the current impact and the last known change.
  2. Collect direct evidence from logs, runtime state, and configuration before changing anything.
  3. Separate immediate recovery from permanent prevention work.
Recovery and prevention

Compare post-failover interface MTU behavior before forcing MTU-ignore everywhere.

Questions worth viewing together
Should I translate commands, logs, or product names?

No. Keep commands, logs, file names, APIs, and product names unchanged, then explain the reasoning in the selected UI language.

What should the answer focus on?

State the root cause, the evidence that supports it, and the safest recovery direction.

Why can the scenario remain in the original language?

The source scenario is treated as an incident artifact. Guidance, checklist, hints, and explanations can be localized around it.