3 Common UDP Ports and Services
Learn how UDP ports identify conventional services and distinguish the common ports, roles, and session-specific behavior of DNS, DHCP, TFTP, NTP, SNMP, and RTP/RTCP.
and port roles
(User Datagram Protocol) provides a lightweight, connectionless way for applications to send datagrams. It does not guarantee delivery, order, or retransmission, so applications that need those behaviors must provide them or use another transport.
ports identify the application service receiving a datagram. A familiar port number indicates a conventional service, but it does not prove that the service is running there.
Name lookup and IPv4 configuration
(Domain Name System) uses port 53 for most routine queries, resolving domain names to IP addresses and supporting other lookups. also uses TCP port 53, including for zone transfers and other cases requiring TCP.
(Dynamic Host Configuration Protocol) automatically provides IPv4 configuration, such as an IP address, to clients. The client sends requests to server port 67, and server replies go to client port 68. Remember the order as server first, client second.
File transfer and network time
(Trivial File Transfer Protocol) provides simple file transfers, often for device booting or configuration. A request begins at server port 69; the file exchange then uses transfer ports selected for that session. has no built-in login or access control, so it requires careful restriction.
(Network Time Protocol) synchronizes computer clocks with time servers and uses port 123.
Network management
(Simple Network Management Protocol) supports monitoring and managing network devices. Managers commonly query agents on port 161, while notification receivers commonly listen on port 162 for traps or other notifications. The port roles can be remembered as queries first, notifications second.
Real-time audio and video
supports real-time audio and video, including voice calls and streaming media. RTP often runs over , with RTCP carrying control and reception reports.
does not use one universal port for every session. Applications or signaling negotiate or select ports for the session, so these ports are generally dynamic rather than a single fixed standard port.
Port patterns to recognize
The IPv4 server and client ports are 67 and 68, respectively. for IPv6 instead uses port 547 for the server and port 546 for the client.
The common fixed port associations are 53, 67/68, 69, 123, and 161/162. Voice and streaming commonly use RTP over , with ports selected for each session; is notable because it also uses TCP port 53.