[Unit]
Description=SSH Reverse Tunnel
After=network.target

[Service]
Restart=always
RestartSec=20
User=u
ExecStart=/usr/bin/ssh -NT -o ServerAliveInterval=60 -o "ExitOnForwardFailure yes" -R 8888:localhost:22 u@D.D.D.D

[Install]
WantedBy=multi-user.target