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Port53

TransportTCP/UDP

ServiceDNS

Port 53TCP/UDP

Domain name resolution. UDP for the majority of requests, especially for some large responses and zone transfers.

What is Port 53 for?

DNS. The protocol or service generally associated with this is DNS.

Transport Protocol

TCP/UDP

Safety precautions

Avoid open solvers. Protect DNS zone transfers.

Should we open this port in the firewall?

Only if a service is actually needed the use it. Apply the principle of any privilege: limit the authorized sources, destinations and interfaces, and then log connections when relevant.

How do I check this port?

Test-NetConnection SERVER -Port 53

Under Linux, you can use nc -vz SERVER 53.

Port/service associations are common conventions. An application can be configured on another port.