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CompTIA A+ Port Numbers: Memorize port numbers on CompTIA A+ Exam

Sarah Nguyen

Created at August 14, 2025

CompTIA A+ port numbers range from 0 to 65,535. Trying to memorize all of them would be overwhelming and completely unnecessary for the exam. The CompTIA A+ certification focuses on a much smaller set of essential ports that you can easily learn with the right approach. In this guide, you’ll know exactly which ones to focus on and how to remember them quickly. Let’s dive in and make memorizing them easier than you ever thought possible!

What are some CompTIA A+ port numbers you need to know?

Port numbers 20 and 21

In CompTIA A+, ports 20 and 21 are commonly associated with FTP or the File Transfer Protocol. FTP is a generic file transfer protocol that can be used by many different operating systems to transfer information from one device to another, and different types of FTP may use one or both of these protocols. TCP Port 20 is often used for active data transfer, and Port 21 is often used for administration or control.

Port numbers 20 and 21

The FTP protocol often requires some type of authentication into the system, so it may ask for a username, a password, or another type of authentication factor. FTP can also be configured with an anonymous or generic login so that anyone can log in regardless of the username or password. FTP is a full-featured protocol that not only can transfer a file but can also list the files in a directory, add, delete, rename files, and perform other administrative functions.

Port number 22

As part of our tasks as server or network administrators, we are often required to connect to our remote devices and make configuration changes at the command line. To do this securely across the network, we need a protocol that can encrypt all of this data as it’s being sent from one side to the other. The most common protocol used for this is SSH (Secure Shell). It provides an encrypted communication link over TCP Port 22. This is very similar to the old Telnet protocol, but Telnet is one that we commonly no longer see in use because it does not provide encryption. If you’re communicating at the command line to a server, you should always use SSH, and you’ll find that it almost always uses TCP Port 22.

Port number 23

However, you may find older systems on your network that do not support SSH, and the only way to administer that device at the command line is using Telnet. Telnet stands for Telecommunications Network and commonly communicates over TCP Port 23. Visually and functionally, this works the same as SSH: you have a command line, can log in with a username and password, and administer the device remotely. The major difference is that all Telnet communication is in the clear – no encryption is used. That’s why most organizations will block Telnet and recommend SSH instead.

Port number 25

Email continues to be one of the most popular forms of communication across our networks, and to facilitate that, we need a protocol that can send mail from one server to another. That protocol is the Simple Mail Transfer Protocol (SMTP), which commonly uses TCP Port 25. SMTP is used to send email messages from one email server to another, and sometimes devices also send information to email servers using SMTP.

Port number 53

When you type a website address into your browser, you’re not actually connecting to that name directly; you’re connecting to its IP address. To translate a fully qualified domain name (FQDN) into a usable IP address, your device uses the Domain Name System (DNS), which most commonly runs on UDP Port 53.

DNS is essential because you rarely memorize long strings of numbers (IP addresses), but you can easily remember a domain name like example.com. For reliability, multiple DNS servers are usually in place so that domain name resolution stays available even if one server goes down.

Port numbers 67 and 68

When you connect your computer, phone, or tablet to a network, you probably don’t manually type in the IP address, subnet mask, default gateway, or DNS server. Instead, this happens automatically thanks to the Dynamic Host Configuration Protocol (DHCP), which runs on UDP Ports 67 and 68.

Here’s how it works: the DHCP server, either built into your router or running as a standalone server, keeps a pool of IP addresses ready to assign. When your device joins the network, it sends a request, gets an IP address lease for a set period, and can later renew or release that address.

DHCP can even reserve specific IP addresses for important devices like printers, servers, or network-attached storage (NAS), ensuring they always have the same address for easy access.

Port number 69

When you need a simple way to transfer files between devices without authentication, encryption, or advanced features, you use the Trivial File Transfer Protocol (TFTP). TFTP runs on UDP Port 69 and is often used for tasks like booting diskless workstations, updating firmware, or sending configuration files to network devices.

Because TFTP is lightweight and unencrypted, it’s usually only used in secure, internal networks. You won’t use TFTP for sensitive data, but it’s perfect for quick, automated file transfers between trusted devices. Remember: Port 69 = TFTP for small, fast, no-frills transfers.

Port number 80

Every time you browse a website without the padlock icon in your browser, you’re using HTTP over TCP Port 80. HTTP sends data in plain text, meaning it’s not encrypted – anyone monitoring the connection could read it.

This protocol is the backbone of the World Wide Web and is still used today, though most modern sites have upgraded to HTTPS (Port 443) for security. Still, you’ll often see Port 80 used for public web servers, testing environments, or redirecting traffic to a secure HTTPS connection. Remember: Port 80 = standard, unencrypted web traffic.

Port number 110

If you’ve ever downloaded emails from a mail server to your device, you may have used POP3 over TCP Port 110. POP3 downloads messages from the server and, by default, removes them from the server once retrieved.

This makes POP3 great for devices with limited storage or users who want emails stored locally. However, it’s less flexible than IMAP (Port 143), which keeps messages synced across multiple devices.

Port numbers 137 and 139

In older Windows networks, file and printer sharing relied on NetBIOS running over TCP/IP. UDP Port 137 handled the Name Service, which allowed devices to find each other by name instead of IP address. TCP Port 139 managed the Session Service, enabling file transfers and network communication between devices.

Today, NetBIOS is largely replaced by SMB over Port 445, but you may still see Ports 137 and 139 used for backward compatibility in legacy systems.

Port number 143

When you want to keep your email synced across multiple devices, IMAP is the go-to protocol. Running on TCP Port 143, IMAP stores your messages on the mail server and lets you manage folders, mark emails as read, and search through mail – all without downloading everything locally.

Unlike POP3 (Port 110), IMAP keeps your inbox consistent on your phone, laptop, and desktop, making it ideal for modern, multi-device email use. For CompTIA A+, remember: Port 143 = IMAP for synced email access.

Port numbers 161 and 162

If you manage switches, routers, printers, or servers, you’ll use SNMP to monitor and control these devices. UDP Port 161 handles the regular queries and commands to gather information or make configuration changes. UDP Port 162 is used for SNMP Traps, which are alerts sent by the device to a management station when something important happens, like a hardware failure or threshold being exceeded.

SNMP is essential for network administrators because it enables centralized monitoring and automation. Remember: 161 = ask the device, 162 = the device alerts you.

Port number 389

When your network needs to look up user accounts, permissions, or resources in a centralized database, it often uses LDAP over TCP/UDP Port 389. LDAP is the backbone for many directory services, including Microsoft Active Directory, allowing devices and applications to quickly find information about users, groups, printers, or other network resources.

For example, when you log in to a corporate computer, LDAP helps verify your credentials against the central directory. In CompTIA A+ terms, remember: Port 389 = directory lookups and authentication.

Port number 443

Whenever you visit a website with a padlock icon in the browser, you’re using HTTPS over TCP Port 443. HTTPS encrypts web traffic using SSL/TLS, protecting sensitive information like passwords, payment data, and personal details from eavesdropping. Port 443 has replaced Port 80 as the default for modern websites, making secure browsing the standard. For your CompTIA A+ exam, remember: Port 443 = encrypted, secure web traffic.

Port number 445

If you’ve ever mapped a network drive or shared a folder between Windows computers, you’ve used SMB over TCP Port 445. SMB handles file sharing, printer sharing, and other network resource access in Windows environments, without needing NetBIOS Ports 137 and 139. Modern SMB runs directly over TCP/IP on Port 445, making it faster and more efficient. For CompTIA A+, remember: Port 445 = direct Windows file and printer sharing.

Port number 3389

When you’re troubleshooting or managing devices, remote access can save you time and effort. Remote Desktop Protocol (RDP), running on TCP Port 3389, lets you view and control another computer as if you were sitting right in front of it.

While RDP is built into Windows systems, you can also connect from macOS, Linux, Unix, iOS, and other platforms using compatible clients. With RDP, you can manage the entire desktop or run just a single application remotely – making it a versatile tool for IT support and system administration.

FAQs

1. How many port number-related questions are in the CompTIA A+ exam?

The number can vary, but you can typically expect a few questions on port numbers and their associated protocols. These may appear as multiple-choice questions, matching exercises, or scenario-based questions. Knowing the most common ports will help you score quick points.

2. Do I need to know all the port numbers for the CompTIA A+ exam?

No, you don’t need to memorize all 65,535 port numbers. The exam focuses on a core list of around 15 – 20 essential ports. If you understand their purpose and can match each port number to its protocol, you’ll be well-prepared for any port-related question.

Final thoughts

CompTIA A+ port numbers may seem overwhelming at first, but mastering them is easier when you focus on the essentials. Once you feel confident about these ports and their protocols, the best way to test your memory is to try our CompTIA A+ practice test. Practice questions will help you see how these ports appear in real exam scenarios and identify any weak spots before test day.