Autossh

apt install autossh
brew install autossh

• Loop waiting to connect to server: AUTOSSH_POLL=5 AUTOSSH_GATETIME=0 autossh -M 0 -o ServerAliveInterval=5 -o ServerAliveCountMax=1 YOUR_SERVER_NAME_OR_IP

See also

• telnet, netcat, ncat, socat
• ssh clients: ssh (OpenSSH client), putty, plink, mosh, paramiko, conch pssh, sshpass and autossh