TCP/IP networks provide a variety of network services through their Application layer protocols. Network services include electronic mail, Telnet for remote logon, and File Transfer Protocol (FTP) for transferring files across networks.
Each network service is associated with a port. A port is a logical number assigned to a particular service through which the service is requested. Some network services and their common port numbers are listed in Table 16.1.
|FTP Data||20||File Transfer Protocol data|
|FTP Control||21||File Transfer Protocol commands|
|Telnet||23||Telnet remote logon|
|SMTP||25||Simple Mail Transfer Protocol|
|DNS||53||Domain Name Server|
|TFTP||69||Trivial File Transfer Protocol ...|