Port 853: DNS over TLS
TCP 853 is the port for DNS over TLS (DoT). Only on public resolvers you operate.
| Service | DNS over TLS (DoT) |
|---|---|
| Protocol | TCP |
| Exposure risk | Low: normally safe to expose |
| Range | Well-known (0–1023): binding needs root/admin on Unix |
What port 853 does
Encrypted DNS queries to resolvers such as 1.1.1.1, 8.8.8.8 and 9.9.9.9. Android's Private DNS setting uses DoT on 853.
Should port 853 be open?
Only on public resolvers you operate.
Find what's listening on port 853
- Linux:
sudo ss -tulpn | grep :853 - macOS:
sudo lsof -nP -i :853 - Windows:
netstat -ano | findstr :853, then look up the PID in Task Manager.
Open or block it in a firewall
- ufw:
sudo ufw allow 853/tcp(ordeny) - firewalld:
sudo firewall-cmd --add-port=853/tcp --permanent && sudo firewall-cmd --reload - Windows:
New-NetFirewallRule -DisplayName "Port 853" -Direction Inbound -Protocol TCP -LocalPort 853 -Action Allow
Port assignment per the IANA Service Name and Transport Protocol Port Number Registry. Test several ports at once with the port scanner, or any port with the open port checker.
Questions about port 853
What is port 853 used for?
DNS over TLS (DoT). Encrypted DNS queries to resolvers such as 1.1.1.1, 8.8.8.8 and 9.9.9.9. Android's Private DNS setting uses DoT on 853.
Is port 853 TCP or UDP?
TCP. DNS over TLS uses TCP port 853.
Is it safe to open port 853?
Low: normally safe to expose. Only on public resolvers you operate.
How do I check if port 853 is open?
Use the checker on this page: it connects to your host on TCP 853 from the internet. Locally, run
nc -vz host 853 (macOS/Linux) or Test-NetConnection host -Port 853 (PowerShell). To see what is listening on your own machine, run ss -tulpn | grep :853 (Linux) or netstat -ano | findstr :853 (Windows).