A number from 0 through 1023 used to identify a network service on an IP network (the Internet). Residing in a field in the TCP or UDP header, the port number directs packets to the appropriate application in the server. The most well-known port is 80, which identifies HTTP traffic for a Web server. For details about port numbers, see TCP/IP port.
Registered and Private Ports
The Internet Assigned Numbers Authority (IANA) registers ports 1024 to 49151 for the convenience of the Internet community. Port numbers from 49152 to 65535 are private ports, also called "dynamic ports." For the complete list of well-known ports and registered ports, visit www.iana.org/assignments/port-numbers. See port scanning, ICANN and IANA.
COMMON WELL-KNOWN PORTS
Service Port Function
HTTP 80 Web
HTTPS 443 Web (secure)
FTP 20,21 File transfer
FTPS 989,990 File transfer (secure)
Telnet 23 Remote login
SSH 22 Remote login (secure)
DNS 53 Host naming
SMTP 25 Internet mail
POP3 110 Client access
IMAP 143 Client access
NNTP 119 Usenet newsgroups
NNTPS 563 Usenet newsgroups (secure)
IRC 194 Chat
NTP 123 Network time
SNMP 161,162 Network management
CMIP 163,164 Network management
Syslog 514 Event logging
Kerberos 88 Authentication
NetBIOS 137-139 DOS/Windows naming
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