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What are TCP/UDP Ports?

April 26, 2017ports TCP UDP

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What are TCP/UDP Ports?

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TCP and UDP use port numbers for the purpose of identifying applications that are using the service. TCP/IP applications have common ports that they use for communicating. These are called well known ports. Here are some examples: Application Well Known Port Number FTP (file transfer) 20 and 21 Telnet (terminal emulation) 23 SMTP (email) 25 http (web) 80 POP3 (email post office) 110 Applications listen on their well-known ports. If a TCP or UDP message arrives with a destination port number of 80 then a web server application will accept (read) the message, assuming the destination address is the web server’s IP address. Messages that have a port number of 110 will be ignored by the web server app, but the POP3 email server application will listen to those messages. In this context the web server and email server apps are running on the same server hardware with a single IP address. Port Negotiation Hyper Text Transfer Protocol (HTTP) is a good example of port negotiation. Web browsing