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Networking, from packets to production

A self-paced path through how computer networks actually work — from what a packet is, to reading a traceroute, to why a load balancer exists. Every lesson has a short exercise and a knowledge check; nothing here is graded or saved, it just runs in your browser.

// The path

Three stages, seven lessons, foundations to applied troubleshooting. Work through them in order, or jump straight to whatever you need.

// Foundations

Start here if packets, frames and the OSI model are still new words.

  • How data actually moves

    Foundational20 min

    Every request you make online gets broken into packets, wrapped in frames, and handed across physical wires or radio waves. This lesson builds a mental map of that journey using the OSI and TCP/IP models — not to memorize seven layer names, but to know which layer to blame when something breaks.

    By the end, you can

    • Explain what a packet, a frame, and a segment are, and how they nest
    • Match a real problem ("no wifi", "site won't load", "video is choppy") to the layer most likely responsible
    • Describe the difference between the OSI model and the simpler TCP/IP model

    Exercise

    Open a terminal and run "ipconfig /all" (Windows) or "ifconfig" / "ip a" (macOS/Linux). Find your device's IP address, MAC address, and default gateway, and write one sentence describing what each one is for.

    Knowledge check

    A friend says their video call has choppy audio but the picture is fine. Which layer is the most useful place to start looking?

  • Addresses and names

    Foundational25 min

    IP addresses identify machines, MAC addresses identify network interfaces, and DNS translates human-friendly names into IP addresses so nobody has to remember numbers. This lesson covers IPv4 notation, private vs. public ranges, and how a DNS lookup actually resolves.

    By the end, you can

    • Tell a private IP address (192.168.x.x, 10.x.x.x) apart from a public one
    • Describe the steps a resolver takes to turn a domain name into an IP address
    • Explain why a device can share its private IP with thousands of other home routers

    Exercise

    Run "nslookup example.com" (or "dig example.com"). Note the IP address it returns, then run it again for a large site you use daily and compare how many addresses come back.

    Knowledge check

    Why can two different homes both have a device at 192.168.1.10 without conflict?

// Core protocols

The rules that decide how data is delivered, addressed, and secured in transit.

  • TCP vs. UDP: reliability trade-offs

    Intermediate30 min

    TCP guarantees delivery and order at the cost of latency; UDP sends fast and loose with no guarantees. This lesson walks through the TCP three-way handshake, why UDP exists, and which one real applications — downloads, DNS, video calls, games — actually choose, and why.

    By the end, you can

    • Describe the TCP three-way handshake (SYN, SYN-ACK, ACK) in your own words
    • List two applications that prefer UDP and explain the trade-off they are making
    • Explain why retransmission helps a file download but hurts a live video call

    Exercise

    Pick three apps you use daily (a browser, a video call app, an online game). For each, guess whether it mostly relies on TCP or UDP, then check whether you were right.

    Knowledge check

    A live multiplayer game drops a UDP packet describing a player's position from one frame ago. What should the game do?

  • Routing and subnets

    Intermediate35 min

    Routers decide, hop by hop, where a packet goes next. Subnetting carves an address range into smaller networks using a mask, and CIDR notation is the shorthand for that split. This lesson builds enough subnetting fluency to read a /24 and know how many hosts it holds.

    By the end, you can

    • Convert a CIDR prefix (like /24 or /26) into a subnet mask and a host count
    • Explain what a default gateway does when a packet's destination is outside the local subnet
    • Describe, at a high level, how a router picks the next hop for a packet

    Exercise

    Given the network 192.168.10.0/26, work out the number of usable host addresses and the first and last usable host. Check your answer with an online CIDR calculator.

    Knowledge check

    A device wants to reach an address outside its own subnet. Where does it send the packet first?

  • HTTP and TLS

    Intermediate30 min

    HTTP is the request/response language the web speaks; TLS wraps it in encryption so nobody between you and the server can read or tamper with it. This lesson covers HTTP methods and status codes, plus what happens during a TLS handshake before "https://" starts working.

    By the end, you can

    • Match common HTTP status codes (200, 301, 404, 500) to what they tell the client
    • Explain, at a high level, what a TLS handshake achieves (encryption + server identity)
    • Describe why HTTPS protects data in transit, not what happens to it after it arrives

    Exercise

    Open your browser's network devtools, load a page, and inspect one request. Note its method, status code, and response headers, then explain in one sentence what each told you.

    Knowledge check

    A browser padlock icon (HTTPS) mainly tells you that…

// Applied networking

Turning the theory into troubleshooting instinct and design judgment.

  • Diagnosing a broken connection

    Advanced35 min

    When "the internet is down," the fastest fix comes from working outward layer by layer: local link, then gateway, then DNS, then the remote host. This lesson builds a repeatable checklist using ping, traceroute, and DNS lookup tools to isolate where a connection actually fails.

    By the end, you can

    • Use ping and traceroute to tell a local network problem apart from a remote one
    • Build an ordered checklist for triaging "the internet doesn't work"
    • Read a traceroute hop list to spot where latency or loss appears

    Exercise

    Run "traceroute example.com" (or "tracert" on Windows) against two different sites. Compare hop counts and latency, and note which hop, if any, looks like a bottleneck.

    Knowledge check

    You can ping your router but not a public DNS server (e.g. 8.8.8.8). Where does the problem most likely sit?

  • Designing for reliability

    Advanced30 min

    Real systems stay up by planning for failure: load balancers spread traffic across servers, redundant paths remove single points of failure, and latency budgets force explicit trade-offs about where time is spent. This lesson introduces the vocabulary for talking about network reliability at a system level.

    By the end, you can

    • Explain what a load balancer does and why it removes a single point of failure
    • Describe redundancy at the network level (multiple paths, multiple providers) vs. the server level
    • Define a latency budget and give an example of how it constrains a design decision

    Exercise

    Pick a service you rely on (a banking app, a streaming site). In a few bullet points, guess where it likely uses redundancy — servers, network paths, or both — and why that matters to you as a user.

    Knowledge check

    A load balancer sitting in front of three identical web servers mainly helps with…

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