FAQ Is UPnP safe, and which ports does Rtorrent 16 open on my router?

[Silas Mariusz]

Symptoms

• The router's list of UPnP mappings shows entries with the description "Rtorrent 16".
• You want to know what Rtorrent 16 asks the router for before you leave UPnP on.

Cause
By default, UPnP and PCP / NAT-PMP are on, so Rtorrent 16 asks the router to forward ports to the NAS's LAN address. It asks for the BitTorrent port (TCP and UDP) and the DHT port (UDP). It asks for the panel's ports (TCP) only if you turn on WebUI ports, which is off by default. It asks for the mobile port (TCP) while Remote access for the phone apps is on, unless you turn off Mobile ports. Only paired phones get an answer on that port. When Network & NAT finds a second router in front of yours, Rtorrent 16 also asks that router for the same ports over PCP or NAT-PMP. When you stop Rtorrent 16, it removes the mappings it made.


Resolution

1. See what the router granted. Open Network & NAT. In the Network services card, Mapped as shows each mapping, and By shows the method.
2. Check the switches. Open Settings → Port forwarding & VPN and look under Router port mappings. Leave WebUI ports off unless you need the panel from the internet. Its help warns: "Can expose the panel's login to the internet. Set your own password first."
   
   
3. If you do not want automatic mappings, disable UPnP and PCP / NAT-PMP. Press Review & save and confirm the changes. Rtorrent 16 then removes the mappings it made. Forward the BitTorrent port (TCP and UDP) and the DHT port (UDP) manually on the router instead.

Notice & Advise

• When Rtorrent 16 requests its own Let's Encrypt certificate for the panel and port 80 is not forwarded yet, it asks the router to forward TCP port 80 to the NAS while the request runs. It removes the mapping afterwards. It does this even with both switches off.
• Knock knock on the WhatsApp and Telegram pages is off until you turn it on. While it is on, writing "knock knock" to the bot maps a random port to the panel's https port for a few minutes.

Ref. links:
Rtorrent 16 guide: Ports