---
title: "The port is open after a start, but closed some hours later"
url: "https://forum.qnap.net.pl/threads/the-port-is-open-after-a-start-but-closed-some-hours-later.46309/"
thread_id: 46309
date: "2026-11-11"
category: "FAQ"
section: "Knowledge base"
source: "Forum QNAP Polska"
site: "https://forum.qnap.net.pl"
language: "pl"
ai_policy: "https://forum.qnap.net.pl/ai-policy.md"
license: "https://forum.qnap.net.pl/ai-policy.md"
---

# The port is open after a start, but closed some hours later

> Source: <https://forum.qnap.net.pl/threads/the-port-is-open-after-a-start-but-closed-some-hours-later.46309/> · FAQ · Forum QNAP Polska · 2026-11-11

**Symptoms**

- After Rtorrent 16 starts, **Network & NAT** shows **IPv4 TCP port … open**.
- Some hours later, it shows **IPv4 TCP port … not reachable**.

**Cause**
A router keeps an automatic port mapping only for a limited time. Rtorrent 16 requests a PCP or NAT-PMP mapping for one hour. A UPnP mapping lasts until the router forgets it, for example when the router restarts. Every five minutes, the Rtorrent 16 watchdog checks the mappings. With **PCP / NAT-PMP** on, it requests every mapping again for another hour. With only **UPnP** on, it reads the router's UPnP table and requests again any mapping that the router no longer has. A lost mapping therefore returns within five minutes if the router accepts the request.

**Resolution**

1. Check the switches. In **Settings → Port forwarding & VPN**, under **Router port mappings**, enable **PCP / NAT-PMP** and **UPnP** if your router supports them. Both are on by default.
![](https://forum.qnap.net.pl/attachments/75939/)
2. Wait up to five minutes. Then open **Network & NAT** and press **Check TCP port**. **Mapped as** in the **Network services** card shows what the router granted.
3. Read the log. Open **Diagnostics** and select **service** under **File** in the **Logs** card. With only UPnP on, a lost mapping leaves a line such as "port forwarding: the router no longer had the UPnP mapping for …; mapped again". If the line ends with "not mapped again", the router refused the new request.
4. If the router keeps refusing, forward the ports manually on the router: the BitTorrent port over TCP and UDP, and the DHT port over UDP, to the NAS's LAN address.

**Notice & Advise**

- When you stop Rtorrent 16, it removes the mappings it made. It requests them again at the next start.
- The QNAP System Logs get a port forwarding line only when something changes, for example when the router starts refusing a mapping.

Ref. links:
[Rtorrent 16 guide: Ports](https://pub.qnaputilities.com/rtorrent16/demo/guides/?g=ports)

---

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