portdesc

Ports between 1024 and 49151 are considered "registered". This means that they can be "reserved" (in a very loose sense of the word) for certain services by issuing a request to the IANA (Internet Assigned Numbers Authority). They are not strictly enforced, but they can give a clue as to the possible services running on a certain port.
Ports between 49152 and 65535 cannot be registered and are suggested for private use.


However, there are some ports that are worth knowing due to their ubiquity. The following is only a very incomplete list:

20: FTP data
21: FTP control port
22: SSH
23: Telnet <= Insecure, not recommended for most uses
25: SMTP
43: WHOIS protocol
53: DNS services
67: DHCP server port
68: DHCP client port
80: HTTP traffic <= Normal web traffic
110: POP3 mail port
113: Ident authentication services on IRC networks
143: IMAP mail port
161: SNMP
194: IRC
389: LDAP port
443: HTTPS <= Secure web traffic
587: SMTP <= message submission port
631: CUPS printing daemon port
666: DOOM <= This legacy FPS game actually has its own special port