| Port Number | Associated Protocol (or Keyword) | TCP/UDP Usage | Secure Version and Port | Usage |
| 21 | FTP | TCP | FTPS, port 989/990 | Transfers files from host to host. |
| 22 | SSH | TCP or UDP | Secure Shell: Remotely administers network devices and systems. Also used by Secure Copy (SCP) and Secure FTP (SFTP). | |
| 23 | Telnet | TCP or UDP | Remotely administers network devices (deprecated). | |
| 25 | SMTP | TCP | SMTP with SSL/TLS, port 465 or 587 | Sends e-mail. |
| 49 | TACACS+ | TCP | Remote authentication. Can also use UDP, but TCP is the default. Compare with RADIUS. |
|
| 53 | DNS | TCP or UDP | DNSSEC | Resolves hostnames to IP addresses and vice versa. |
| 69 | TFTP | UDP | Basic version of FTP. | |
| 80 | HTTP | TCP | HTTPS (uses SSL/TLS), port 443 | Transmits web page data. |
| 88 | Kerberos | TCP or UDP | Network authentication, uses tickets. | |
| 110 | POP3 | TCP | POP3 with SSL/TLS, port 995 | Receives e-mail. |
| 119 | NNTP | TCP | Transports Usenet articles. | |
| 135 | RPC/epmap/ dcom-scm | TCP or UDP | Used to locate DCOM ports. Also known as RPC (Remote Procedure Call). | |
| 137–139 | NetBIOS | TCP or UDP | Name querying, sending data, NetBIOS connections. | |
| 143 | IMAP | TCP | IMAP4 with SSL/TLS, port 993 | Retrieval of e-mail, with advantages over POP3. |
| 161 | SNMP | UDP | Remotely monitor network devices. | |
| 162 | SNMPTRAP | TCP or UDP | Traps and InformRequests are sent to the SNMP Manager on this port. | |
| 389 | LDAP | TCP or UDP | LDAP over SSL/TLS, port 636 | Maintains directories of users and other objects. |
| 445 | SMB | TCP | Provides shared access to files and other resources. | |
| 514 | Syslog | UDP | Used for computer message logging, especially for router and firewall logs. A secure version (Syslog over TLS) uses TCP as the transport mechanism and port 6514. |
|
| 860 | iSCSI | TCP | IP-based protocol used for linking data storage facilities. Also uses port 3260 for the iSCSI target. |
|
| 1433 | Ms-sql-s | TCP | Opens queries to Microsoft SQL server. | |
| 1701 | L2TP | UDP | VPN protocol with no inherent security. Often used with IPsec. | |
| 1723 | PPTP | TCP or UDP | VPN protocol with built-in security. | |
| 1812/1813 | RADIUS | UDP | An AAA protocol used for authentication (port 1812), authorization, and accounting (port 1813) of users. Also, ports 1645 and 1646. |
|
| 3225 | FCIP | TCP or UDP | Encapsulates Fibre Channel frames within TCP/IP packets. Contrast with Fibre Channel over Ethernet (FCoE), which relies on the data link layer and doesn’t rely on TCP/IP directly. |
|
| 3389 | RDP | TCP or UDP | Remotely views and controls other Windows systems. | |
| 3868 | Diameter | TCP (or SCTP) | An AAA protocol; can replace the RADIUS protocol. |