Networking and Security books

I’m about to set up a couple of VPS instances running OpenSUSE LEAP 15.2, but I’d like to improve my knowledge of networking and security in general before I do this. I’ve been running LEAP 15.2 on my laptop for a few weeks, and I think I’ve mostly got the hang of things, but if people could recommend some books to read on networking and security to get me from a beginner to an intermediate user, I would be grateful.

I want to be able to understand things like VLANs and VPNs and TCP/IP as a whole and how to secure systems that are directly connected to the internet.

Once upon a time before the Internet there were only printed books and because of the cost and limited access it was important to choose your books wisely.

Today, there are numerous works published and accessible for free on the Internet, and to a certain extent the ability to search for what you need on the Internet has become as critical to your overall skillset as the topic itself. Just use a good search engine and pick through the top results. If the one you’re reading is less comprehensible, drop it and on to the next which will be written a little differently and maybe easier for you to understand.

Round out your learning by discussing and asking questions. If you don’t have actual people around you whom you can share info with, again use the Internet. Find others and post questions. For myself, in the earlier years of the Internet after Bulletin Boards, mail lists dedicated to System Administration were very popular. Today, before the current pandemic User Groups and Meetups were good places to find others with common interest close by.

And, of course practice.
Set up laboratories.
Before virtualization, you’d have to invest in a few thousand dollars’ worth of equipment or find someone who would be willing to let you set up things on their machines (again, at least several thousand dollars’ worth).
Today, with virtualization the cost is only a little more storage and maybe a little more RAM and you can set up multiple laboratories to get basic experience with system administration.

BTW - I recommend setting aside but not ignoring security topics in the beginning.
Learn how to set up things properly, that’s part of security but real understanding of security depends on a great many things… First an expertise in setting things up that minimize security problems, then basic concepts and then graduating to more advanced topics. Modern security is recognized to be multi-layer, and often requires at least devops and possibly Development knowledge. Although basic security concepts are actually relatively few, how those concepts are applied can be complex, and like regular System Administration can be different for those who simply maintain vs those who architect.