Common TCP/UDP Ports for CompTIA A+ Core 1 (220-1101)

To pass the CompTIA A+ Core 1 exam, you must memorize essential common TCP UDP ports, including DNS (53), HTTP (80), HTTPS (443), SSH (22), and RDP (3389). Understanding these ports allows you to troubleshoot network connectivity, configure firewalls, and secure remote access in real-world IT support scenarios.

Why do you need to memorize common TCP UDP ports for the A+?

If you've looked at the 220-1101 objectives, you know that networking is a massive pillar of the Core 1 exam. In the real world, ports are the 'doors' that allow specific types of traffic to enter or leave a device. If you don't know which door a service uses, you can't configure a firewall or troubleshoot why a user can't reach a server.

CompTIA doesn't just want you to memorize a list; they want you to apply this knowledge to scenarios. You'll see questions where a technician is troubleshooting a web server that isn't responding—knowing whether to check port 80 or 443 is the difference between a pass and a fail. To help you drill these into your brain, we provide 1,000 expert-curated practice questions at Cert Sensei that put these ports into actual troubleshooting contexts.

How do DNS and DHCP handle network addressing?

Let's start with the infrastructure basics: DNS and DHCP. Domain Name System (DNS) operates on port 53. It's essentially the phonebook of the internet, translating human-readable names like google.com into IP addresses. While it primarily uses UDP for fast queries, it uses TCP for zone transfers between servers. If a user can ping an IP but can't load a website, port 53 is the first place you should look.

Then you have Dynamic Host Configuration Protocol (DHCP), which uses ports 67 (server) and 68 (client). DHCP is what allows a device to automatically get an IP address, subnet mask, and default gateway the moment it plugs into a network. Without ports 67 and 68 functioning, your devices will default to an APIPA address (169.254.x.x), which is a classic red flag on the A+ exam.

What is the difference between HTTP and HTTPS for web traffic?

You use these every day, but for the exam, you need to be precise. Hypertext Transfer Protocol (HTTP) uses port 80. It sends data in plaintext, meaning anyone sitting in the middle of the connection can read your passwords or credit card numbers. In a modern enterprise environment, port 80 is mostly used to redirect users to a secure connection.

Hypertext Transfer Protocol Secure (HTTPS) uses port 443. It wraps standard HTTP traffic in an encrypted layer using SSL/TLS. From a troubleshooting perspective, if you can access a site via HTTP but get a timeout on HTTPS, you're likely dealing with a certificate issue or a firewall blocking port 443. Remember, security is a recurring theme in the 220-1101 objectives, so always prioritize the encrypted port in your answers.

Why should you use SSH over Telnet for remote management?

When you need to manage a switch or a Linux server remotely, you have two main choices: SSH and Telnet. Telnet operates on port 23 and is a relic of a simpler time. It sends everything—including your administrative password—in cleartext. In any real-world scenario or exam question, Telnet is the 'wrong' answer if security is mentioned.

Secure Shell (SSH) uses port 22 and provides a secure, encrypted channel for remote command-line access. It's the industry standard for a reason. If the exam asks you how to securely manage a network device from a remote location, SSH on port 22 is your go-to. We emphasize these security distinctions in our detailed expert reasoning for every practice question we offer, ensuring you understand the 'why' and not just the number.

How do RDP and SMB facilitate Windows networking?

For those working in Windows environments, Remote Desktop Protocol (RDP) and Server Message Block (SMB) are essential. RDP uses port 3389, allowing you to take full graphical control of a remote computer. It's incredibly powerful, but exposing port 3389 directly to the internet is a massive security risk that often leads to ransomware attacks.

SMB, on the other hand, uses port 445. This is the protocol used for file and printer sharing across a local network. When you map a network drive or open a shared folder on a server, SMB is doing the heavy lifting. If a user can't access a shared folder but can ping the server, you should immediately check if port 445 is being blocked by the Windows Defender Firewall.

How can you effectively study these ports without burning out?

Rote memorization is boring and often fails under the pressure of a timed exam. Instead, use active recall. Group the ports by function: Web (80, 443), Remote Access (22, 23, 3389), and Infrastructure (53, 67, 68). Create flashcards that describe the scenario first (e.g., 'Secure remote CLI access') and force yourself to recall the port number (22).

Finally, leverage performance analytics. At Cert Sensei, our platform doesn't just tell you if you got a question wrong; we provide domain-level tracking. If your analytics show you're struggling specifically with the 'Networking' domain, you can use our custom quiz builder to filter for only those topics. This targeted approach saves you dozens of study hours by focusing your energy where it's actually needed.

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