Networking and diagnostics

Debug network failures from the application outward. First confirm the destination and port, then name resolution, route selection, local firewall policy, remote reachability, and protocol behavior.

Useful observations

ss or netstat shows listeners and connections, dig or getent checks name resolution, and curl can test an HTTP path with headers and timing. Packet captures are powerful but should be scoped by interface, host, and port to avoid collecting unnecessary sensitive data.

Remote access

SSH keys, host verification, least-privilege accounts, and restricted forwarding reduce the blast radius of remote administration. Avoid putting secrets in command arguments or shell history.