Port 853 — DNS over TLS

Port 853 — TCP

DNS queries protected by TLS.

What is port 853 used for?

Encrypted DNS resolution over TLS.

Transport protocol

TCP

Security precautions

Control which DNS resolvers are allowed by the organization's policy.

Should we open this port in the firewall?

Allow this port only when a required service uses it. Apply least privilege: restrict authorized sources, destinations and interfaces, and log connections where appropriate.

How do I check this port?

Test-NetConnection SERVER -Port 853

On Linux, nc -vz SERVER 853 checks TCP connectivity only. A successful TCP connection does not validate the application, authentication or TLS configuration.

Port-to-service mappings are common conventions. Applications can use a different configured port; confirm the actual service and transport.