Port 853: DNS over TLS
Port 853 is DNS over TLS, which encrypts DNS queries between a client and resolver to stop eavesdropping and tampering on the network path. It is the dedicated-port alternative to DNS over HTTPS, which instead shares port 443.
| Port number | 853 |
|---|---|
| Service | DNS over TLS (DoT) |
| Protocol | TCP |
| Category | Core services |
| Default encryption | Yes (TLS/SSH) |
How do I check whether port 853 is open?
Port 853 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 853 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 853 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':853 ' | Lists the process bound to port 853 on Linux. On macOS use lsof -nP -iTCP:853 -sTCP:LISTEN, on Windows netstat -ano | findstr :853 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 853 used for?
Port 853 is DNS over TLS, which encrypts DNS queries between a client and resolver to stop eavesdropping and tampering on the network path. It is the dedicated-port alternative to DNS over HTTPS, which instead shares port 443.
Is port 853 TCP or UDP?
Port 853 (DNS over TLS) uses TCP.
Is port 853 secure?
Yes. Port 853 carries encrypted traffic by default, so data in transit is protected.
Should I open port 853 on my firewall?
Only if you specifically need DNS over TLS. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.