If you have a NAT router which supports UPnP, the easiest way to get a working port forward is to make sure UPnP setting is enabled on both Syncthing and the router – Syncthing will try to handle the rest. If it succeeds you will see a message in the console saying:
Created UPnP port mapping for external port XXXXX on UPnP device YYYYY.
If this is not possible or desirable you should set up a port forward for port 22000/TCP, or the port set in the Sync Protocol Listen Address setting. The external forwarded port and the internal destination port has to be the same (i.e. 22000/TCP).
Communication in Syncthing works both ways. Therefore if you set up port forwards for one device, other devices will be able to connect to it even when they are behind a NAT network or firewall.
In the absence of port forwarding, Relaying may work well enough to get devices connected and synced, but will perform poorly in comparison to a direct connection.
If your PC has a local firewall, you will need to open the following ports for incoming and outgoing traffic:
Port 22000/TCP (or the actual listening port if you have changed the Sync Protocol Listen Address setting.)
Port 21027/UDP (for discovery broadcasts on IPv4 and multicasts on IPv6)
Uncomplicated Firewall (ufw)¶
If you’re using
ufw on Linux and have installed the Syncthing package, you can allow the necessary ports by running:
sudo ufw allow syncthing
If you also want to allow external access to the Syncthing web GUI, run:
sudo ufw allow syncthing-gui
Allowing external access is not necessary for a typical installation.
You can then verify that the ports mentioned above are allowed:
sudo ufw status verbose
In case you installed Syncthing manually you can follow the instructions to manually add the syncthing preset to ufw.
If you are using [Firewalld](https://www.firewalld.org) it has included support for syncthing (since version 0.5.0, January 2018), and you can enable it with
sudo firewall-cmd –zone=public –add-service=syncthing –permanent sudo firewall-cmd –reload
Similarly there is also a syncthing-gui service.
Remote Web GUI¶
To be able to access the web GUI from other computers, you need to change the
GUI Listen Address setting from the default
0.0.0.0:8384. You also need to open the port in your local firewall if you
Tunneling via SSH¶
If you have SSH access to the machine running Syncthing but would rather not open the web GUI port to the outside world, you can access it through a SSH tunnel instead. You can start a tunnel with a command like the following:
ssh -L 9999:localhost:8384 machine
This will bind to your local port 9999 and forward all connections from there to port 8384 on the target machine. This still works even if Syncthing is bound to listen on localhost only.