FAQ Network & NAT shows another port than the one my router forwards

[Silas Mariusz]

Symptoms

• Network & NAT shows another port than the one you forwarded on the router.
• The Dashboard shows a red badge such as Port … was busy · running on …, or the DHT port reads (moved from …).

Cause
Network & NAT shows the port that rtorrent really listens on. The saved setting is a range, 50000-50010 by default, and rtorrent listens on one port in that range. With Pick a random port from the range on, that port changes at every start. If other programs hold every port in the saved range when rtorrent starts, rtorrent takes the nearest free port within the 20 ports above the range for that start only. The saved setting stays the same, and the next start tries it again. The DHT port also moves when another program holds it, to the first free UDP port above the saved one. In both cases, with UPnP or PCP / NAT-PMP on, Rtorrent 16 asks the router to forward the new port. With Ask the VPN for an incoming port on, rtorrent listens on the port that the VPN gave.


Resolution

1. See the ports in use. On the Dashboard, the Network card shows Listening port and DHT port. A moved port shows (moved from …) after the number. Hover over the red badge to see which program holds the saved port.
   
   
2. Set the port that your router forwards. Open Settings → Connection. With Pick a random port from the range off, the field reads Listening port (1024-65535). Enter the forwarded port; for example, 42000 saves the range 42000-42000. Alternatively, forward the whole range on the router. Press Review & save and confirm the change. If a notice says that a restart is needed, press Apply now.
   
   
3. If another program holds the port, stop that program. The next start of rtorrent takes the saved port again.
4. Open Network & NAT and press Check TCP port.

Notice & Advise

• In the Network services card, two numbers under Mapped as (… → …) mean that the router gave another outside port. Use the same port on both sides.
• If Settings shows the red notice "rtorrent currently listens on port …. Saved port range: …. Saved changes may still need a restart.", the notice only compares the two ports. It does not tell why they differ.

Ref. links:
Rtorrent 16 guide: Ports