SSH Uses TCP, Not UDP: What to Allow Through Your Firewall
If a firewall rule asks whether SSH should use TCP or UDP, choose TCP . Standard OpenSSH connects over TCP, usually on port 22. That applies to remote shells as well as file transfers made with SFTP or SCP. The distinction matters when you configure a host firewall, router, or cloud security group: allowing UDP 22 does not enable a normal SSH connection. The practical firewall rule For a typical…
If you encounter a firewall rule asking whether to allow SSH over TCP or UDP, choose TCP as the transport. By default, OpenSSH servers use TCP port 22 for standard remote shells and file transfers with SFTP or SCP. Allowing UDP port 22 will not enable a normal SSH connection. When configuring firewall settings, ensure you allow inbound TCP traffic to the correct SSH port.
For non-default ports, replace the port number accordingly. A failed TCP connectivity test does not necessarily mean you need a UDP rule, as other factors like authentication or server configuration could prevent successful SSH login. Standard SSH uses TCP for both general connections and file transfer protocols like SFTP and SCP.
Tools that leverage SSH, such as port forwarding, carry TCP connections through SSH. While some remote terminal tools use UDP for their sessions, this does not imply that standard OpenSSH operates over UDP. The IANA port registry can be misleading; a UDP entry for SSH does not represent the default behavior of a standard OpenSSH server.
To troubleshoot SSH connection issues, verify the server is configured to listen on the expected TCP port and ensure the firewall or network permits the TCP connection.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
