Why Does a Linux Server Reject Connections After Its Firewall Rule Was Added?

A firewall rule can appear present but fail to allow traffic because of rule order, the wrong interface or address family, a separate cloud firewall, or a service listening only locally.

What to check

Check the listening socket, host firewall chain and counters, interface, source and destination addresses, IPv4 and IPv6 paths, and any upstream network policy. Keep an existing management session open while inspecting remote access rules.

Recommended next step

Adjust only the verified rule and test from the intended source. Informatix Systems can troubleshoot Linux networking and server security.