Port 853 supports DNS over TLS and domain-s (UDP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
DNS queries protected by TLS.
Clients or forwarding resolvers using an encrypted channel to a recursive DNS service.
Client to server
Validate the resolver identity and account for policy controls that may otherwise rely on observing traditional DNS traffic.
domain-s (UDP reference coverage) is documented as a network service convention for port 853 over UDP.
Use this reference entry when identifying or validating systems documented to use 853/UDP.
Varies
Confirm the listening process and current vendor documentation before permitting traffic; a listed convention does not prove the active service or its security posture.