This article looks at common port numbers and their associated services, and which transport protocol they use.
One of the many fundamental things to know as a server administrator is some common services’ functions and port numbers. Just as the IP address identifies the computer, the network port identifies the application or service running on the computer.
I’m sure you’ve heard the term “port” before, but what does it mean in the world of computers?
What’s a Network Port?
In computer networking, a port is a communication endpoint. Typically, ports identify a specific network service assigned to them. Within an operating system, the primary use of a port number is to transfer the data between a computer network and an application.
Port numbers range from 0 to 65535. They are divided into three sub-ranges:
- Well-known ports (0-1023) – assigned to specific service by IANA (Internet Assigned Numbers Authority). Only privileged programs that run as root on Linux systems can use ports under 1024.
- Registered ports (1024-49151) – ports that an organization can register with IANA to be used for a particular service.
- Dynamic ports (49152-65535) – used by client programs.
There are two primary transport protocols in networking that uses port numbers -TCP and UDP.
TCP stands for Transmission Control Protocol. It is a connection-oriented protocol. Before exchanging data, the communicating devices should establish a connection and then shut it.
TCP is the most widely used networking protocol. It is incredibly dependable, and it is used for everything from browsing the web to sending emails and file transfers.
UDP stands for User Datagram Protocol. It is a connectionless protocol. This is due to the lack of overhead associated with creating, maintaining, and terminating connections. For broadcast and multicast network transmission, UDP is a good choice.
Common TCP and UDB Default Ports
Following are some of the common TCP and UDP default ports.
21 (TCP, UDP) – FTP
Port 21 is commonly associated with FTP (File Transfer Protocol). FTP is for transferring files between a client and a server. It is usually regarded as a “non-secure” file transfer protocol.
FTP sends data in clear text and provides an anonymous option that does not require a password. However, FTP is a trusted and widely used protocol for transferring files.
22 (TCP, UDP) – SSH
SSH, or Secure Shell Protocol, is a network communication protocol used to perform operations on remote computers, but it may also be used for transferring data. Whenever we run a command through default SSH port number 22, a connection between client and server is established.
SSH was developed as a safe substitute for the unencrypted Telnet protocol, and it utilizes cryptographic techniques to ensure that all communication to and from the remote server is encrypted.
23 (TCP) – Telnet
Port 23 is typically used by the Telnet protocol. The protocol is often used for an administrative command-line interface in networking equipment such as routers and switches.
However, because the protocol is unencrypted, it is usually only used safely within a local area network, as the data is in cleartext.
25 (TCP) – SMTP
Port 25 is the original standard email SMTP (Simple Mail Transfer Protocol) port and the oldest since it first debuted in 1982. After four decades, SMTP on port 25 is the basic standard for sending email via the internet between mail servers.
53 (TCP, UDP) – DNS
DNS (Domain Name System) turns domain names into IP addresses. As a result, people may type ordinary words into their browsers without remembering the IP address for each website, thanks to DNS servers.
DNS has been designed to use both UDP and TCP port 53, with UDP being the default, and falls back to using TCP when it cannot communicate on UDP.
67,68 (UDP) – DHCP
DHCP (Dynamic Host Configuration Protocol) provides network addresses to dynamically configured hosts on a TCP/IP network. It uses UDP ports 67 and 68. Port 67 should be used by the server and port 68 by the client.
80 (TCP) – HTTP
Port 80 is the port number assigned to the commonly used internet communication protocol HTTP (Hypertext Transfer Protocol). The HTTP protocol defines the format for communication between internet browsers and websites.
In other words, port 80 uses to send and receive page requests from a webserver. The web traffic that passes through the port remains in plain text.
110 (TCP) – POP3
POP3 (Post Office Protocol version 3) is a mail protocol used to retrieve mail from a remote server to a local email client. It is a relatively simple mail protocol, making it less prone to errors and more straightforward implementation. The default POP3 port is 110.
111 (TCP, UDP) – Portmapper
Portmapper service is required to run NFS both on the client and the server-side. It runs on port 111 for both TCP and UDP protocols. Portmap makes the dynamic binding of remote programs possible.
137 (TCP, UDP) – NetBIOS
Port 137 is utilized by NetBIOS (Network Basic Input/Output System) Name service. NetBIOS’s primary purpose is to allow applications on different computers to communicate and establish sessions to access shared resources like files and printers and locate each other via a local area network (LAN).
143 (TCP, UDP) – IMAP
IMAP (Internet Message Access Protocol) is a mail protocol used to access email on a local client’s remote web server. The IMAP protocol works on port 143, the default IMAP non-encrypted port.
161, 162 (UDP) – SNMP
The SNMP (Simple Network Administration Protocol) protocol suite is a collection of network management and monitoring protocols. It is often used to monitor firewalls, routers, switches, servers, printers, bridges, NAS disks, UPS, and other network devices.
SNMP ports are utilized via UDP on port 161 for SNMP Managers communicating with SNMP Agents and via UDP on port 162 when agents send unsolicited SNMP traps to the SNMP Manager.
443 (TCP) – HTTPS
HTTPS stands for HyperText Transfer Protocol Secure. Port 443, a web browsing port, is primarily used for HTTPS services. It is a port that billions of people across the globe use every single day. Over 95% of secured websites use HTTPS via port 443 for secure data transfer.
587 (TCP) – SMTP
Port 587 is the standard secure SMTP (Simple Mail Transfer Protocol) port. It is the default mail submission port. This is the one that will provide the best results when users submit an email to be routed via a proper mail server.
The use of port 587 in conjunction with TLS encryption ensures that email is sent securely and following the IETF’s requirements.
993 (TCP) – IMAPS
IMAPS (IMAP over SSL) means IMAP traffic travels over a secure socket to a secure port. When using an encrypted IMAP connection, the default port is 993. It helps ensure your safety and privacy on the internet.
You should now understand that network ports are given by the TCP or UDP protocols. A port is a number that is used to uniquely identify a network transaction by defining both the host and the service. They are necessary to differentiate between many different IP services.
See RFC 1700 or IANA for a complete list of network port numbers for more information.