What are TCP and UDP?

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the two main ways data travels across networks. TCP sets up a connection, numbers the packets and resends lost ones, so everything arrives complete and in order; websites, e-mail and file transfers use it. UDP just sends packets without checking, which is faster and suits voice calls, video, DNS lookups and some newer web traffic. For security tools, the difference matters: a TCP connection shows a clear start and end, while UDP traffic must be grouped by the tool. Scans and floods can use either.

← All 69 questions on What is…? Network and security termsAll topics