# /etc/systemd/system/ssh-tunnel.service
[Unit]
Description=Persistent SSH port-forward tunnel
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=YOUR_USER

ExecStart=/usr/bin/ssh \
    -NT \
    -L 127.0.0.1:22:127.0.0.1:22100 \
    -o ServerAliveInterval=30 \
    -o ServerAliveCountMax=3 \
    -o ExitOnForwardFailure=yes \
    user@SSH_HOST

Restart=always
RestartSec=5

[Install]
WantedBy=multi-user.target