Books on Computer Networking are often intimidating - thousands of pages, boring diagrams... This colorful series walks you through the networking basics in just a few thousand words! It also offers hands-on labs to practice the obtained knowledge. I wish I had such a condensed resource at my disposal during my university days.
As a software engineer, I need to deal with networking every now and then - be it configuring a SOHO network, setting up container networking, or troubleshooting connectivity between servers in a data center. The domain is pretty broad, and the terminology can get quite confusing quickly. This article is my layman's attempt to sort the basic things out with the minimum words and maximum drawings. The primary focus will be on the Data link layer (OSI L2) of wired networks where the Ethernet is the king nowadays. But I'll slightly touch upon its neighboring layers too.
Gee, it's my turn to throw some gloom light on iptables! There are hundreds or even thousands of articles on the topic out there, including introductory ones. I'm not going to put either formal and boring definitions here nor long lists of useful commands. I would rather try to use layman's terms and scribbling as much as possible to give you some insights about the domain before going to all these tables, rules, targets, and policies. By the way, the first time I faced this tool I was pretty much confused by the terminology too!
SSH is yet another example of an ancient technology that is still in wide use today. It may very well be that learning a couple of SSH tricks is more profitable in the long run than mastering a dozen Cloud Native tools destined to become deprecated next quarter.
One of my favorite parts of this technology is SSH Tunnels. With nothing but standard tools and often using just a single command, you can achieve the following:
And more 😍
But despite the fact that I use SSH Tunnels daily, it always takes me a while to figure out the right command. Should it be a Local or a Remote tunnel? What are the flags? Is it a local_port:remote_port or the other way around? So, I decided to finally wrap my head around it, and it resulted in a series of labs and a visual cheat sheet 🙈
The difference between these two networking devices has been an unsolvable mystery to me for quite some time. For a while, I used to use the words "bridge" and "switch" interchangeably. But after getting more into networking, I started noticing that some people tend to see them as rather different devices... So, maybe I've been totally wrong? Maybe saying "bridge aka switch" is way too inaccurate?
Let's try to figure it out!
In Ethernet, all the nodes forming one L2 segment constitute a broadcast domain. Such nodes should be able to communicate using their L2 addresses (MAC) or by broadcasting frames. A broadcast domain is a logical division of a computer network. Multiple physical (L1) segments can be bridged to form a single broadcast domain. Multiple L2 segments can also be bridged to create a bigger broadcast domain.
It's pretty common for an L2 segment to have a single IP subnet running atop. However, technically it's possible to configure multiple IP subnets over a single L2 broadcast domain. And although more complicated, configuring a single IP subnet over multiple disjoint L2 segments is also doable. In this lab, we'll cover the first two scenarios while the more advanced third case deserves its own lab - Proxy ARP.
In Ethernet Lab - Broadcast domain we learned how to use switches (bridges) to merge multiple L2 segments into a single broadcast domain. In this lab, we'll see how to use the VLAN capabilities of a switch to split a single broadcast domain into multiple smaller domains.
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