Chai Prep

Computer networking

See what really happens on the wire.

A full course, from a single fetch() down to the wire and back up through TCP, DNS, HTTP and TLS. Every step is drawn out as a clear visual, so the network stops being a black box.

Start with the introductionSee all 31 chapters
The seven OSI layers numbered 7 down to 1.Chapter 10, The TCP/IP & OSI ModelsThe OSI model (7 layers)
31
chapters
3
parts
231
illustrated pages
5
hours of reading

What the course covers

31 chapters in 3 parts.

Read them in order, or jump to the topic you need. Every section pairs a clear written explanation with a drawn page you can take in at a glance.

Networking notes: Why networking matters for developersStart hereIntroduction to NetworkingWhy networks matter to developers, and the road aheadWhy networking matters for developersWhat happens when you make an HTTP request?Networking fundamentals, our base layerHow routing worksICMP, ping and tracerouteTransport layer: UDP12 sections · 9 min

Part B

Protocols

Routing, ICMP, TCP and UDP, DNS, HTTP, TLS, DHCP and NAT.

17 chapters

  1. Networking notes: Why layer the network at all?Chapter 10The TCP/IP & OSI ModelsThe layered map that organizes every protocol you have met so far7 sections · 9 min
  2. Networking notes: What routing actually isChapter 11How Routing Works (In Depth)Routing tables, hop-by-hop forwarding, and why the MAC changes but the IP does not7 sections · 10 min
  3. Networking notes: What is ICMP?Chapter 12ICMP: ping & tracerouteThe internet’s status-and-error protocol, and the tools you already use built on it7 sections · 9 min
  4. Networking notes: What is UDP?Chapter 13UDP: The Fast ProtocolConnectionless, no guarantees, tiny overhead, and perfect for the right jobs6 sections · 7 min
  5. Networking notes: The datagram = header + dataChapter 14Anatomy of a UDP DatagramThe whole UDP header is just four fields and eight bytes6 sections · 6 min
  6. Networking notes: What is TCP?Chapter 15TCP: The Reliable BackboneConnection-oriented delivery, the 3-way handshake, and the graceful close7 sections · 9 min
  7. Networking notes: Two countersChapter 16TCP Sequence & Acknowledgement NumbersThe counters that make delivery reliable and in-order7 sections · 9 min
  8. Networking notes: The TCP segment headerChapter 17TCP Segment, MTU, MSS & FragmentationThe segment header, size limits on the wire, and what happens when data is too big7 sections · 10 min
  9. Networking notes: The problemChapter 18TCP Flow ControlThe sliding window that stops a fast sender from drowning a slow receiver7 sections · 8 min
  10. Networking notes: The congestion problemChapter 19TCP Congestion ControlHow TCP avoids melting the network, slow start, AIMD, and ECN8 sections · 9 min
  11. Networking notes: The internet’s phone bookChapter 20DNS: How Resolution WorksFrom a name to an IP by walking the root, TLD, and authoritative servers7 sections · 9 min
  12. Networking notes: What is a DNS record?Chapter 21DNS Records & Email SecurityThe record types you will actually configure, and how they stop email spoofing8 sections · 10 min
  13. Networking notes: HTTP = request / responseChapter 22HTTP & Its VersionsFrom HTTP/1.1 to HTTP/3, how the web’s core protocol got faster7 sections · 9 min
  14. Networking notes: HTTP cannot pushChapter 23WebSocketsA persistent, two-way channel for real-time apps6 sections · 7 min
  15. Networking notes: Why TLS?Chapter 24TLS & HTTPSHow the padlock works: encryption, integrity, and proving who you are talking to6 sections · 9 min
  16. Networking notes: Why DHCP existsChapter 25DHCPHow your device gets an IP the instant it joins a network6 sections · 7 min
  17. Networking notes: Why NAT existsChapter 26NATHow a whole household of devices shares one public IP address6 sections · 8 min

Questions

Good to know.

Who is this course for?
Developers who already know what a server, a frontend and an HTTP request are, but want to see what is really happening underneath. The notes are student-friendly, so it also suits anyone meeting networking for the first time.
How is a chapter laid out?
Each chapter opens with a short introduction, then works through its topic one section at a time. Every section pairs a drawn page with a written explanation, so you can take in the picture first and then read the detail. Some chapters (4 in all) also include an interactive figure you can step through.
How long does it take?
About 5 hours of reading in all, across 231 sections. A chapter takes between 5 and 20 minutes, so one fits comfortably into a study session.

Open the black box.

Start with the introduction for a map of the whole course, then go as deep as you like, one drawn page at a time.

Start with the introductionBrowse the chapters