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Port 53: DNS

Common Ports Reference: What runs on port 3389, 445 or 5985: common TCP and UDP ports for web, mail, Windows, AD, databases and VPNs, with security notes.

The ports that come up when opening a firewall, reading a scan or troubleshooting a connection: what runs on each, TCP or UDP, and what to watch out for. Search by number or name. Port numbers and service names were checked against IANA's port number registry; ports that are widely used but assigned by IANA to something else are marked unofficial.

Port number or name

53 is a system port (0-1023): assigned by IANA, and on Linux only root can listen on it. IANA's registry lists everything assigned to it: look up 53 at IANA.

1 of 96 ports

DNS, DHCP, time, SNMP, logging and VPNs.

PortProtocolServiceWhat it's forIANA name
53
TCP, UDP
DNS
Name lookups. Answers too big for UDP (DNSSEC, large TXT records) retry over TCP 53, so open both.
domain

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