HTTP、FTPといった非常に広く使われているアプリケーションプロトコルでは、 使用するポート番号が決められており、ウェルノウンポート番号（Well-known Port Number）と呼ばれます。 このウェルノウンポート番号は、0〜1023までの番号から割り当てられています。
主なウェルノウンポート番号（TCP）
| ポート 番号 |
サービス名 | 説明 |
| 1 | tcpmux | TCP Port Service Multiplexer |
| 7 | echo | Echo |
| 9 | discard | Discard |
| 11 | systat | Active Users |
| 13 | daytime | Daytime (RFC 867) |
| 17 | qotd | Quote of the Day |
| 19 | chargen | Character Generator |
| 20 | ftp-data | File Transfer [Default Data] |
| 21 | ftp | File Transfer [Control] |
| 22 | ssh | SSH Remote Login Protocol |
| 23 | telnet | Telnet |
| 25 | smtp | Simple Mail Transfer |
| 37 | time | Time |
| 42 | nameserver | Host Name Server |
| 43 | nicname | Who Is |
| 53 | domain | Domain Name Server |
| 70 | gopher | Gopher |
| 79 | finger | Finger |
| 80 | http ( www-http) | World Wide Web HTTP |
| 88 | krb5 kerberos-sec | Kerberos |
| 95 | supdup | SUPDUP |
| 101 | hostname | NIC Host Name Server |
| 102 | iso-tsap | ISO-TSAP Class 0 |
| 109 | pop2 | Post Office Protocol - Version 2 |
| 110 | pop3 | Post Office Protocol - Version 3 |
| 111 | sunrpc | SUN Remote Procedure Call |
| 113 | auth ( ident ) | Authentication Service |
| 115 | sftp | Simple File Transfer Protocol |
| 117 | uucp-path | UUCP Path Service |
| 119 | nntp | Network News Transfer Protocol |
| 123 | ntp | Network Time Protocol |
| 143 | imap | Internet Message Access Protocol |
| 163 | cmip-man | CMIP/TCP Manager |
| 164 | cmip-agent | CMIP/TCP Agent |
| 177 | xdmcp | X Display Manager Control Protocol |
| 179 | bgp | Border Gateway Protocol |
| 194 | irc | Internet Relay Chat Protocol |
| 220 | imap3 | Interactive Mail Access Protocol v3 |
| 389 | ldap | Lightweight Directory Access Protocol |
| 443 | https | http protocol over TLS/SSL |
| 465 | smtps | SMTP over SSL |
| 515 | printer | Printer spooler ( lpr ) |
| 587 | submission | Submission |
| 636 | ldaps | ldap protocol over TLS/SSL |
| 989 | ftps-data | ftp protocol, data, over TLS/SSL |
| 990 | ftps | ftp protocol, control, over TLS/SSL |
| 993 | imaps | imap4 protocol over TLS/SSL |
| 995 | pop3s | pop3 protocol over TLS/SSL |
主なウェルノウンポート番号（UDP）
| ポート 番号 |
サービス名 | 説明 |
| 7 | echo | Echo |
| 9 | discard | Discard |
| 11 | systat | Active Users |
| 13 | daytime | Daytime (RFC 867) |
| 17 | qotd | Quote of the Day |
| 19 | chargen | Character Generator |
| 37 | time | Time |
| 39 | rlp | Resource Location Protocol |
| 42 | Nameserver | Host Name Server |
| 49 | tacacs | Login Host Protocol (TACACS) |
| 53 | domain | Domain Name Server |
| 67 | bootps | Bootstrap Protocol Server |
| 68 | bootpc | Bootstrap Protocol Client |
| 69 | tftp | Trivial File Transfer |
| 88 | krb5 kerberos-sec | Kerberos |
| 111 | sunrpc | SUN Remote Procedure Call |
| 123 | ntp | Network Time Protocol |
| 137 | netbios-ns | NETBIOS Name Service |
| 138 | netbios-dgm | NETBIOS Datagram Service |
| 139 | netbios-ssn | NETBIOS Session Service |
| 161 | snmp | SNMP |
| 162 | snmptrap | SNMPTRAP |
| 177 | xdmcp | X Display Manager Control Protocol |
| 201 | at-rtmp | AppleTalk Routing Maintenance |
| 202 | at-hbp | AppleTalk Name Binding |
| 204 | at-echo | AppleTalk Echo |
| 206 | at-zis | AppleTalk Zone Information |
| 213 | ipx | IPX |
| 520 | router | RIP |
| 546 | dhcpv6-client | DHCPv6 Client |
| 547 | dhcpv6-server | DHCPv6 Server |