Common port numbers need to be memorized by anyone who is looking to work in tech. Once you start working in tech you will memorize these port numbers just because you have to work with them all the time. However, if you are looking to get your foot in the tech industry, having these port numbers memorized can help you land a job. Jobs that reference port numbers include network engineers, IT support, system administrators, web developers, etc.
Likewise, if you are planing on going to school for tech or passing certain certifications, such as the Comptia Network+ or Security+ exams, you should learn these common port numbers.
Each of these numbers is a different port on which machines communicate with one another. This communication happens using different protocols, such as HTTP, SSH, etc. For common protocols, there are standard assigned port numbers that are always the same. Port 80 is always the HTTP port. Anyone who works with devices that communicate with one another ends up knowing these numbers by heart. You cannot help but known them, because you come across them so often.
Remember that a port number is used by a certain protocol, and there protocols use either TCP or UDP. The main difference between TCP and UDP is that TCP is connection oriented. For TCP communication, the recipient verifies that they have received packers. UDP on the other hand is connectionless. UDP packets are sent out, and the sender does not wait or expect any kind of acknowledgement that the packets were received.
Here are the most common port numbers:
| Port | Protocol | TCP/UDP |
|---|---|---|
| 20-21 | FTP | TCP |
| 22 | SSH | TCP |
| 23 | Telnet | TCP |
| 25 | SMTP | TCP |
| 53 | DNS | UDP |
| 67/68 | DHCP | UDP |
| 80 | HTTP | TCP |
| 110 | POP3 | TCP3 |
| 123 | NTP | UDP |
| 143 | IMAP | TCP |
| 161/162 | SNMP | UDP |
| 443 | SSL (HTTPS) | TCP |
| 587 | SMTP | TCP |
| 993 | IMAP (SSL) | TCP |
| 995 | POP3 (SSL) | TCP |
Generally anything over port 1000 you will never need to memorize, unless it is very specific to your job.
When I got my first tech job I knew maybe three of the above port numbers by heart. Today I know all of the above by heart, plus a few others, just because I come across them at work on a regular basis.
If nothing else, the above list is helpful when setting up a firewall. Knowing which ports to allow and which to block is important in keeping your network and devices secure.
