NAT and Port Mapping
BitTorrent works best when other peers can open connections to you. Home routers block unsolicited inbound traffic by default (that’s NAT), which leaves you connectable only to peers you dialed first — fewer peers, slower torrents. Port mapping fixes this: Motrix asks your router to forward its BT/DHT ports automatically.
Enabling port mapping
In Settings → Network → NAT mapping:
| Setting | Meaning |
|---|---|
| Enable port mapping | Open inbound BT/DHT ports on the router automatically |
| Preferred protocol | auto (recommended), or force pcp, natpmp, or upnp |
| Mapping TTL (seconds) | How long each mapping lease lasts before renewal (1200–7200) |
The mapping applies to the BT listen port and DHT listen port configured in Settings → BitTorrent. With auto, Motrix negotiates the most capable protocol your router speaks — PCP first, then NAT-PMP, then UPnP.
Note
Your router must have UPnP, NAT-PMP, or PCP enabled. Many routers ship with UPnP on; some security-hardened setups turn it off, in which case you can forward the ports manually in the router instead.
The NAT tile
The Dashboard’s NAT tile is mission control: current state, detected NAT type, External IP, active Mappings, and a Health grade (Good / Fair / Poor). Its buttons — Enable NAT / Disable NAT, Force remap, Run diagnostic — cover the day-to-day operations, and the stats bar on the Downloads page has a quick NAT toggle too.
Understanding NAT status
| Status | Meaning |
|---|---|
| Off | Automatic port mapping is disabled or stopped |
| Initializing | Motrix is discovering the gateway, waiting for the download engine, creating mappings, or waiting for an automatic retry |
| Active | The BT and DHT mappings were created and Motrix will renew their leases |
| Failed | Discovery or mapping still failed after the automatic retry budget was exhausted |
During recovery, the tile may show Retrying 1/3, 2/3, or 3/3. Let these retries finish before treating the incident as terminal. A network change, such as reconnecting Wi-Fi or rebooting the router, also triggers a fresh discovery attempt.
Important
NAT Failed does not mean the download engine failed. HTTP downloads and outbound BitTorrent connections can continue. The main effect is reduced inbound peer connectivity, which may mean fewer peers or slower torrent performance.
If NAT shows Failed
Work through these checks in order:
- Confirm that the download engine says Ready. NAT maps the BT and DHT ports owned by aria2. If the engine is still starting or restarting, wait for it to become ready, then choose Enable NAT again.
- Use
autoas the preferred protocol. This lets Motrix try PCP, NAT-PMP, and UPnP instead of being locked to one protocol your router may not support. - Check the router setting. Enable at least one of UPnP, NAT-PMP, or PCP on the router. The wording and location vary by manufacturer. Apply the router change, then choose Force remap in Motrix.
- Check for a port conflict. Another computer, a second Motrix instance, or another BitTorrent client may already own the same external port. Close the other client or change the BT and DHT listen ports in Settings → BitTorrent, save, and retry.
- Temporarily rule out network intermediaries. VPN clients, virtual network adapters, guest Wi-Fi, mobile hotspots, enterprise networks, and some firewall suites can hide the real gateway or block mapping traffic. Reconnect on the normal home network and retry.
- Check for double NAT or CGNAT. Compare the router’s WAN address with the public address reported by an IP-checking service. Private WAN ranges such as
10.0.0.0/8,172.16.0.0/12,192.168.0.0/16, and carrier-grade100.64.0.0/10usually mean another NAT layer exists upstream. - Use manual port forwarding as a fallback. Reserve the computer’s LAN address, forward the configured TCP BT port and UDP DHT port to it, and keep those Motrix ports stable. You may then disable automatic NAT mapping.
After correcting the network or router configuration, Enable NAT starts a clean discovery and mapping attempt. Force remap rebuilds the current mappings. If the state becomes Active and later falls back to Failed, inspect router lease settings, router restarts, VPN changes, and whether the computer moved to another network.
Tip
On a trusted home network, auto is the best default. On public or untrusted networks, leave automatic port mapping off unless you understand the exposure and control the gateway.
NAT type detection
With “Enable detection via STUN” on, Motrix queries STUN servers to classify your NAT:
| NAT type | What it means for BitTorrent |
|---|---|
| Open | You’re directly reachable — nothing to fix |
| Full cone | Easily traversable; port mapping makes you fully connectable |
| Restricted / Port restricted | Common home NAT; port mapping helps a lot |
| Symmetric | Hardest case — often carrier-grade NAT (CGNAT); mapping your router may not be enough |
| Blocked | UDP is blocked entirely |
The STUN server list is editable. Privacy note: detection sends queries to third-party STUN servers.
Warning
If the tile’s External IP doesn’t match the WAN IP your router reports, you’re likely behind carrier-grade NAT — your ISP shares one public address among many customers. Port mapping on your own router can’t make you reachable in that case; the rest of BitTorrent still works, just with fewer inbound peers.
Port reachability probe
“Probe port from external service” verifies the mapping end-to-end: an external HTTPS endpoint tries to reach your mapped port and reports whether it’s actually open from the internet. The endpoint list is editable, and — same privacy note — the probe talks to a third-party service.
Auto diagnostic
“Run diagnostics on schedule” controls the periodic diagnostic interval (300–86400 seconds). Run diagnostic on the NAT tile requests an immediate check. Diagnostics provide evidence about NAT type and reachability; they do not bypass CGNAT, enable a disabled router protocol, or replace manual port forwarding when automatic mapping is unavailable.