Managing port security
Ports of Call

© Photo by Jamie O'Sullivan on Unsplash
A few basic commands for working with ports can help you make your small network or standalone system more secure.
Ports are a core feature of modern computing. I'm not talking about transferring versions of applications to another architecture or operating system. Instead, I mean the kind of port that is an address for a virtual connection point to or from a computer and another device or server, including the Internet. Ports direct external traffic to the correct application, and this function makes them important for troubleshooting and security. How do you find which ports are open or listening (i.e., currently in use) when there is no need for them to be? What ports are associated with which application or server? How do you know whether any ports are hidden and being used by an intruder? Even if you are working on a standalone computer, knowing how to answer these questions is a basic administrative skill.
Ports can be either hardware or software. Either way, they are treated similarly. Most ports are managed by two protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Both TCP and UDP have a range of port numbers, divided into three categories:
- System ports (numbers 0-1023): These are the most common ports and essential to external communication. Sometimes called well-known ports, system ports can only be used by root or privileged users. For example,
ssh
is port 22, and the Network Time Protocol (NTP) is port 123. While these ports can be changed, the changed ports can only communicate with other machines that have also reassigned their ports accordingly. - Registered ports (numbers 1024-49151): These ports are available for processes and applications run by ordinary users. Registered ports are sometimes called user ports.
- Dynamic ports (numbers 49152-65535): These ports can be used by any processes or applications as needed, and they are assigned on the fly. Dynamic ports are also called private or ephemeral ports.
[...]
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Find SysAdmin Jobs
News
-
Kubuntu Focus Announces XE Gen 2 Linux Laptop
Another Kubuntu-based laptop has arrived to be your next ultra-portable powerhouse with a Linux heart.
-
MNT Seeks Financial Backing for New Seven-Inch Linux Laptop
MNT Pocket Reform is a tiny laptop that is modular, upgradable, recyclable, reusable, and ships with Debian Linux.
-
Ubuntu Flatpak Remix Adds Flatpak Support Preinstalled
If you're looking for a version of Ubuntu that includes Flatpak support out of the box, there's one clear option.
-
Gnome 44 Release Candidate Now Available
The Gnome 44 release candidate has officially arrived and adds a few changes into the mix.
-
Flathub Vying to Become the Standard Linux App Store
If the Flathub team has any say in the matter, their product will become the default tool for installing Linux apps in 2023.
-
Debian 12 to Ship with KDE Plasma 5.27
The Debian development team has shifted to the latest version of KDE for their testing branch.
-
Planet Computers Launches ARM-based Linux Desktop PCs
The firm that originally released a line of mobile keyboards has taken a different direction and has developed a new line of out-of-the-box mini Linux desktop computers.
-
Ubuntu No Longer Shipping with Flatpak
In a move that probably won’t come as a shock to many, Ubuntu and all of its official spins will no longer ship with Flatpak installed.
-
openSUSE Leap 15.5 Beta Now Available
The final version of the Leap 15 series of openSUSE is available for beta testing and offers only new software versions.
-
Linux Kernel 6.2 Released with New Hardware Support
Find out what's new in the most recent release from Linus Torvalds and the Linux kernel team.