Well-know ports

Well-known ports--0 through 1023: Controlled and assigned by the Internet Assigned Numbers Authority (IANA), and on most systems can be used only by system (or root) processes or by programs executed by privileged users. The assigned ports use the first portion of the possible port numbers. Initially, these assigned ports were in the range 0-255. Currently, the range for assigned ports managed by the IANA has been expanded to the range 0-1023.