User Datagram Protocol (UDP) explained
The User Datagram Protocol (UDP) is a communication protocol for data transmission. It is used mostly for establishing low-latency and loss-tolerant connections between applications on the Internet. The IP address works with TCP and UDP, sometimes called TCP/IP and UDP/IP. Both TCP and UDP send short packets of data called datagrams.
User Datagram Protocol (UDP) Low Overhead vs Reliability
User Datagram Protocol provides the basic transport layer functions. It sends the packets with lower bandwidth overhead and latency than TCP. User Datagram Protocol (UDP) is not a connection-oriented protocol, so it does not offer sophisticated retransmission, flow control, and sequencing mechanisms for lost and out-of-order packets. So, the User Datagram Protocol (UDP) is less reliable than TCP. However, this does not mean that applications that use the User Datagram Protocol (UDP) are forever unreliable and substandard. It only means that the transport layer protocol does not provide these functions and must be implemented in a different place if required.
Because of low overhead, UDP is the best protocol for network applications in which apparent latency is critical, such as gaming, voice, and video communications, which can bear some data loss without badly disturbing apparent quality. Like TCP, UDP does not set up a connection before sending data; it just starts sending data when required.
UDP Datagram reassembly
UDP datagrams arrive at the destination using different routes and arrive in the wrong order. The UDP does not follow sequence numbers, just like TCP. It has no mechanism to reorder the datagram into its transmission order. So, the UDP reassembles the data in the exact order. If the sequence is important to the application, the application should identify the right sequence number and decide how the data should be processed.
Test UDP reassembly with a streaming app: On Windows, use netstat -u -a to check port 5004 (RTP); on Linux, use ss -u -l -p to verify, ensuring application-level reordering.
UDP Server Processes and Requests
UDP-based server applications assign well-known or registered port numbers just like TCP. When these applications and processes run on a server, they accept the data matched with the assigned port number. When UDP receives a datagram destined for one of these ports, it forwards the application data to the proper application based on its port number.
UDP Client Processes
The client application will ask a server process to start communication between the server and the client. The UDP client selects a port number from the range of port numbers randomly. The destination port on the server is generally the well-known or registered port number assigned to the server process. Once the client selects the source and destination ports, the header of all datagrams uses this selected pair of ports. The destination and source ports are reserved for the datagram header when returning the data from the server to the client.
Security Considerations
UDP’s lack of authentication makes it vulnerable to spoofing. Use firewalls (e.g., netsh advfirewall add rule name=”Block UDP 123″ dir=in protocol=UDP localport=123 on Windows or sudo ufw deny 123/udp on Linux) to secure NTP ports, critical for 2025.
Troubleshooting Tips
If datagrams are dropped, check with ping -n (Windows) or ping -c (Linux) for network issues.
For port conflicts, use netstat -u -a (Windows) or ss -u -l (Linux) and reassign ports.