Learning path · 9 lessons · about 5 h
How the internet works
Linux gets you onto a server. Knowing how the internet works is what lets you fix it when "the site is down" and nobody knows why. This path is about the ideas underneath every server, cloud and container: how a name becomes an address, how a packet finds its way, and what really happens between typing a URL and seeing a page. They work the same whatever the operating system, so you'll use them for the rest of your career.
Is this path for you?
You only need to be comfortable in a terminal:
- Moving around and reading files (Linux Basics, lesson 6, Linux Basics, lesson 8)
- Using sudo (Linux Basics, lesson 12)
- Your server's address and gateway (Linux Sysadmin, lesson 1) helps, but isn't required
Finished Linux Basics? Then you're ready. It also fits right next to Linux Sysadmin.
What's ahead
| Lesson | You'll learn to… |
|---|---|
| lesson 1: packets & layers | see every layer of the stack, from the cable and MAC addresses up, and test the MTU |
| lesson 2: IP addresses & subnets | read any address and prefix, tell neighbours from strangers, spot the special ranges, and split a network into smaller ones |
| lesson 3: routing & NAT | read a routing table, follow a packet across the internet, add (and save) a route to another network, and see NAT at work |
| lesson 4: DNS | read dig like a pro, follow a name from the root servers down, and explain why a DNS change takes time to reach everyone |
| lesson 5: TCP, UDP & ports | find every open port, watch a TCP handshake in tcpdump, and tell "refused" from "timed out" |
| lesson 6: HTTP up close | read requests and responses, know your status codes, use virtual hosts, and debug a proxy with curl |
| lesson 7: TLS & certificates | read certificates and chains, diagnose the four classic HTTPS errors, and trust your own CA |
| lesson 8: load balancers & CDNs | put HAProxy in front of three servers, let health checks hide a broken one, and read a CDN cache |
| lesson 9: troubleshooting | a bottom-up method for any network problem, and a real multi-layer outage to fix |
| Then | the final challenge: one server, every layer broken |
How this path works
- Ideas first, tools second. Each lesson explains how something works, then you prove it with real tools:
dig,ping,traceroute,curl,ssandtcpdump. - Side by side only when it differs. DNS and TCP are the same everywhere, so most of this path is written once. Where Rocky and Ubuntu really do something differently (like where a server keeps its DNS settings), you'll see both, side by side as usual.
- A practice network. The practice terminal comes with a small pretend internet: a home router, public DNS servers and a club website that just moved. Break it as much as you like; Reset builds it again.