| 7 | Echo | TCP/UDP | Echoes back any data sent to it. Used for testing and measurement. | RFC 862 |
| 9 | Discard | TCP/UDP | Silently discards all data sent to it. Used for testing. | RFC 863 |
| 9 | Wake-on-LAN | UDP | Wake-on-LAN magic packets are broadcast to this port to remotely power on computers. | — |
| 11 | Systat | TCP/UDP | Returns information about current system users. | RFC 866 |
| 13 | Daytime | TCP/UDP | Returns the current date and time as a human-readable string. | RFC 867 |
| 17 | QOTD | TCP/UDP | Quote of the Day — returns a short ASCII message for amusement or inspiration. | RFC 865 |
| 19 | Chargen | TCP/UDP | Character Generator — streams a continuous sequence of characters. Used for testing. | RFC 864 |
| 20 | FTP Data | TCP | File Transfer Protocol data transfer channel — carries the actual file content. | RFC 959 |
| 21 | FTP Control | TCP | File Transfer Protocol control channel — sends commands and receives responses. | RFC 959 |
| 22 | SSH | TCP | Secure Shell — cryptographic network protocol for secure remote login and command execution. | RFC 4251 |
| 23 | Telnet | TCP | Bidirectional interactive text-oriented communication. Largely replaced by SSH due to lack of encryption. | RFC 854 |
| 25 | SMTP | TCP | Simple Mail Transfer Protocol — used for sending email between mail servers. | RFC 5321 |
| 37 | Time | TCP/UDP | Returns the current time as a 32-bit integer (seconds since 1 Jan 1900). Predecessor to NTP. | RFC 868 |
| 42 | WINS / nameserver | TCP/UDP | Host Name Server — maps hostnames to addresses. Also used by Windows Internet Name Service. | RFC 811 |
| 43 | WHOIS | TCP | Queries databases that store registered users of internet resources such as domain names. | RFC 3912 |
| 49 | TACACS | TCP/UDP | Terminal Access Controller Access Control System — provides centralised authentication. | RFC 1492 |
| 53 | DNS | TCP/UDP | Domain Name System — translates human-readable domain names to IP addresses. | RFC 1034 |
| 67 | DHCP (server) | UDP | Dynamic Host Configuration Protocol — server port for assigning IP addresses to clients. | RFC 2131 |
| 68 | DHCP (client) | UDP | Dynamic Host Configuration Protocol — client port for receiving IP configuration from a server. | RFC 2131 |
| 69 | TFTP | UDP | Trivial File Transfer Protocol — a simple, lockstep protocol for transferring files with no authentication. | RFC 1350 |
| 80 | HTTP | TCP | HyperText Transfer Protocol — the foundation of data communication on the World Wide Web. | RFC 9110 |
| 88 | Kerberos | TCP/UDP | Network authentication protocol using tickets to allow nodes to prove their identity securely. | RFC 4120 |
| 109 | POP2 | TCP | Post Office Protocol v2 — an older protocol for retrieving email from a server. | RFC 937 |
| 110 | POP3 | TCP | Post Office Protocol v3 — retrieves email from a remote server to a local client. | RFC 1939 |
| 115 | SFTP (legacy) | TCP | Simple File Transfer Protocol — a legacy, unsecured file transfer protocol (not SSH File Transfer Protocol). | RFC 913 |
| 118 | SQL Services | TCP/UDP | SQL Services — early assignment for SQL-based database communications. | — |
| 119 | NNTP | TCP | Network News Transfer Protocol — distributes, retrieves, and posts Usenet news articles. | RFC 3977 |
| 123 | NTP | UDP | Network Time Protocol — synchronises clocks between computer systems over packet-switched networks. | RFC 5905 |
| 135 | MS RPC / DCE | TCP | Microsoft Remote Procedure Call / DCE endpoint mapper — used by Windows DCOM services. | — |
| 143 | IMAP | TCP | Internet Message Access Protocol — accesses and manages email directly on a mail server. | RFC 9051 |
| 156 | SQL Service | TCP/UDP | SQL Service — another early assignment for SQL-based database access. | — |
| 161 | SNMP | UDP | Simple Network Management Protocol — collects and organises information about devices on networks. | RFC 1157 |
| 162 | SNMP Trap | TCP/UDP | SNMP notifications (traps) sent from agents to the management system. | RFC 1157 |
| 179 | BGP | TCP | Border Gateway Protocol — manages routing between autonomous systems on the internet. | RFC 4271 |
| 194 | IRC | TCP/UDP | Internet Relay Chat — real-time text communication over the internet. | RFC 1459 |
| 220 | IMAPv3 | TCP | Internet Message Access Protocol version 3 — an older IMAP revision. | RFC 1203 |
| 280 | HTTP-MGMT | TCP | HTTP Management — used for web-based management interfaces. | — |
| 311 | Apple WebAdmin | TCP | Apple macOS Server Admin — web-based administration of Apple server products. | — |
| 318 | TSP | TCP/UDP | PKIX Time Stamp Protocol — provides a trusted timestamping service for digital signatures. | RFC 3161 |
| 389 | LDAP | TCP/UDP | Lightweight Directory Access Protocol — accesses and maintains distributed directory information services. | RFC 4511 |
| 433 | NNSP | TCP | Network News Server Protocol — used for news server-to-server transfers. | — |
| 443 | HTTPS | TCP | HTTP Secure — HTTP over TLS/SSL, the encrypted version of HTTP used for secure web traffic. | RFC 9110 |
| 445 | SMB | TCP | Server Message Block — used for file and printer sharing in Windows networks. Also used by Samba. | — |
| 464 | Kpasswd | TCP/UDP | Kerberos Change/Set Password protocol. | RFC 3244 |
| 465 | SMTPS | TCP | SMTP over implicit TLS — secure email submission, preferred over STARTTLS on port 587. | RFC 8314 |
| 496 | PIM-RP-DISC | UDP | Protocol Independent Multicast — Rendezvous Point Discovery. | — |
| 500 | IKE / ISAKMP | UDP | Internet Key Exchange — negotiates and manages IPsec security associations. | RFC 7296 |
| 512 | rexec | TCP | Remote Process Execution — executes commands on a remote host without encryption. | — |
| 513 | rlogin | TCP | Remote Login — allows users to log in to a Unix host over a network, without encryption. | RFC 1282 |
| 514 | Syslog | UDP | Standard for message logging — allows devices to send event messages across an IP network. | RFC 5424 |
| 515 | LPD / LPR | TCP | Line Printer Daemon — a protocol for submitting print jobs to a remote printer. | RFC 1179 |
| 520 | RIP | UDP | Routing Information Protocol — uses hop count to determine the best path between networks. | RFC 2453 |
| 543 | Klogin | TCP | Kerberos-authenticated remote login. | — |
| 544 | Kshell | TCP | Kerberos-authenticated remote shell. | — |
| 546 | DHCPv6 (client) | UDP | DHCPv6 client port for receiving IPv6 configuration from a server. | RFC 8415 |
| 547 | DHCPv6 (server) | UDP | DHCPv6 server port for assigning IPv6 addresses to clients. | RFC 8415 |
| 548 | AFP | TCP | Apple Filing Protocol — Apple's proprietary network file system protocol for macOS. | — |
| 554 | RTSP | TCP/UDP | Real Time Streaming Protocol — controls streaming media servers for audio and video delivery. | RFC 7826 |
| 563 | NNTPS | TCP | Network News Transfer Protocol over TLS — secure version of NNTP for Usenet news. | RFC 4642 |
| 587 | SMTP Submission | TCP | Email submission — used by mail clients to submit outgoing mail to a server. | RFC 6409 |
| 591 | FileMaker Web | TCP | FileMaker 6.0 and later Web Sharing. Used as an alternative to port 80. | — |
| 593 | HTTP-RPC-EPMAP | TCP | HTTP RPC endpoint mapping, used by Microsoft DCOM services. | — |
| 601 | Syslog over TCP | TCP | Reliable syslog — transmits log messages over a reliable TCP connection. | RFC 3195 |
| 623 | IPMI / RMCP | UDP | Intelligent Platform Management Interface / Remote Management Control Protocol. | — |
| 631 | IPP / CUPS | TCP | Internet Printing Protocol — manages print jobs and queues. Used by CUPS on Linux and macOS. | RFC 8011 |
| 636 | LDAPS | TCP | LDAP over TLS — secure version of LDAP for encrypted directory queries. | RFC 4513 |
| 749 | Kerberos Admin | TCP/UDP | Kerberos administration port — used for administering the Kerberos database. | — |
| 829 | PKIX-3 CA/RA | TCP | Certificate Management Protocol — used between CAs and RAs in PKI deployments. | RFC 4210 |
| 832 | NETCONF over HTTPS | TCP | NETCONF network management protocol over HTTPS. | RFC 5539 |
| 873 | rsync | TCP | rsync file synchronisation protocol — efficient file transfer and sync using delta encoding. | — |
| 981 | SofaWare HTTPS | TCP | SofaWare Technologies Remote HTTPS management. | — |
| 989 | FTPS Data | TCP | FTP over TLS — data channel for encrypted file transfer. | RFC 4217 |
| 990 | FTPS Control | TCP | FTP over TLS — control channel for encrypted file transfer commands. | RFC 4217 |
| 993 | IMAPS | TCP | IMAP over TLS — secure version of IMAP for encrypted email retrieval. | RFC 9051 |
| 995 | POP3S | TCP | POP3 over TLS — secure version of POP3 for encrypted email retrieval. | RFC 1939 |
