Port 20: FTP data
Data channel of active-mode FTP.
- Port
- 20
- Protocol
- TCP
- Service
- FTP data
- Exposure
- Do not expose to the internet
What is port 20 used for?
Moving file contents when an FTP session uses active mode.
Is it safe to expose port 20 to the internet?
FTP sends everything, including passwords, in clear text. Prefer SFTP (port 22) or FTPS.
If port 20 seems closed or unreachable
- Check that the FTP data service is running and listening on port 20, not only on 127.0.0.1.
- Check the firewall on the host itself (Windows Defender Firewall, iptables, nftables, ufw) for a rule that allows TCP 20.
- If the host is behind a router, confirm the forwarding rule points to the correct internal address and that your internet provider does not use carrier-grade NAT.
- Test from outside your own network. A port can be open locally and blocked at the edge, or the other way round.
Using port 20 safely
Treat port 20 as an internal-only service. Reach it through a VPN or an SSH tunnel, restrict it by source address, and keep the software that listens on it patched.
Check whether port 20 is open on your host
The check connects from our server, so it shows what the internet can reach.
Open the port checker