Play PSP ad-hoc games over Tailscale with PPSSPP

Tailscale creates a virtual LAN (a tailnet) so PPSSPP clients in different places can use PPSSPP's built-in ad-hoc server, as described in PPSSPP's LAN/VPN guide. Tailscale also has official clients for phones, which is useful if you run PPSSPP on Android or iOS. This is for PPSSPP. It is not a documented way to put a real PSP onto Tailscale.

Set up Tailscale

1. Install Tailscale on every device from the official download page and sign in, following the quickstart.
2. Confirm that every device appears on the same tailnet.
3. Note the host's Tailscale IP (it starts with 100.). You can see it in the Tailscale client or the admin console. That is the address other players will enter in PPSSPP.

Configure PPSSPP

These steps follow PPSSPP's LAN/VPN ad-hoc instructions. Use the same PPSSPP version on every device when you can.

1. Open Settings > Networking and enable Enable Networking/WLAN.
2. Disable Try to use server-provided packet relay on every player.
3. Disable Enable UPnP on every player (you do not need port forwarding on a virtual LAN).
4. Set Port offset to the same value on every player. If you are unsure, use 10000.
5. On the host only: open the PRO ad-hoc server address option, use Toggle List to find your VPN IP (not your normal LAN IP), and enable Enable built-in PRO ad hoc server. Then start the game and host or wait in the lobby until you see "Network Initialized".
6. On everyone else: set the PRO ad-hoc server address to the host's VPN IP, keep the built-in ad-hoc server disabled, and join the host's game. Do not type leading zeros in the IP (use 192.168.1.1, not 192.168.001.001).

Do not use localhost as the server address when players are on different devices.

Source for the PPSSPP steps: How to play multiplayer games with PPSSPP.