F5400 - Invalid or Unexpected Response from F5 BIG-IP

Agent error code #F5400 indicates that the F5 BIG-IP returned a response the agent could not interpret: a body that did not parse as the expected iControl REST JSON, or an unexpected HTTP status that did not map to a more specific code.

Common causes include:

• Something other than the BIG-IP management API is answering at the configured URL (for example a reverse proxy, captive portal, or load-balanced data-plane address)
• A device software version whose iControl REST responses differ from what the agent expects
• A partial or truncated response from a device under stress

Steps to Resolve

Confirm the URL Targets iControl REST

1. Confirm the F5 BIG-IP URL in the Knocknoc backend points at the management interface, not a virtual server or proxy
2. Confirm /mgmt/shared/authn/login and the data-group endpoint are served by the BIG-IP itself

Check Device Health and Version

1. Check the BIG-IP for control-plane health issues that could truncate responses
2. Note the device software version when contacting support

Still Having Issues?

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