Curated port reference

Port 53: DNS

DNS commonly uses port 53 over TCP + UDP. Review its purpose, traffic direction and operational security considerations.

53TCP + UDP

DNS

Domain-name queries, responses and zone-transfer traffic.

Typical use

UDP handles most queries; TCP is required for zone transfers and responses that do not fit the negotiated UDP size.

Traffic direction

Client to server

Security considerations

Restrict recursion and zone transfers, patch resolvers, and account for both transports in firewall and monitoring policy.

Domain Name SystemActive Directory