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Networking stops being abstract the moment you watch a packet move.

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Everything on the syllabus

34 lessons 8 tracks 17 tools 6 labs 89 practice questions

  • What is a network?
  • LANs, WANs & topologies
  • The OSI Model
  • The TCP/IP stack
  • IPv4 addressing
  • Subnetting & CIDR
  • IPv6 addressing
  • NAT & private ranges
  • Ethernet & MAC addresses
  • How switches learn
  • VLANs & trunking
  • Spanning Tree Protocol
  • How routing decisions work
  • Static vs dynamic routing
  • OSPF basics
  • BGP in plain English
  • How DNS resolves a name
  • DHCP & leases
  • HTTP & TLS
  • NTP & syslog
  • Wireshark basics
  • The CLI toolkit
  • Reading packet captures
  • Building a home lab
  • Cisco IOS basics & CLI modes
  • Configuring VLANs in IOS
  • Static routes & OSPF in IOS
  • ACLs in IOS
  • Reading show command output
  • CIA triad & common attacks
  • Firewalls & ACLs
  • VPN basics
  • Zero Trust & segmentation
  • Logging & monitoring

Start here

Three ways in, depending on why you came

Not sure which fits? Answer a few questions and get sent to the lesson that matches what you already know.

Recommended New to networking Start at lesson one 8 tracks and 34 lessons in the order they build on each other. Each ends in something you do rather than recite. First stop: What is a network? Exam coming up Studying for CCNA or Network+ Go straight to practice: 89 questions in four formats, plus a subnetting drill scored against the clock. First stop: Exercises Working already Need a tool right now 17 tools that open and run: subnet maths, DNS and MAC lookups, packet headers, and real ping and traceroute. First stop: All tools

How a lesson works

Networks make sense when you watch traffic move

Most courses hand you definitions: “Layer 3 is the network layer.” True, and useless on its own. Here you follow one real request, and the definitions attach themselves to things you have seen.

  1. 01

    Read the idea

    Short lessons in a fixed order. Each builds on the last, with no forward references.

  2. 02

    Watch it move

    Every concept is anchored to a real packet, capture or tool output, not a diagram of a diagram.

  3. 03

    Run it yourself

    Lessons end with a tool to run or a capture to read, because the next stop is a ticket queue, not a lecture hall.

  4. 04

    Prove it, then prove it again

    Questions you miss come back on a schedule until you stop missing them.

Hands-on toolkit

Real network tools, running on this page

Not a screenshot: type an address and watch it resolve. The tools you would run in a terminal, with no install and no sign-up.

All 17 tools

Subnet Calculator

Full IPv4 and CIDR maths, including the /31 point-to-point edge case. Type any address with a prefix and every value updates as you type.

Open the full calculator
subnet.calcruns locally

Edit the address. It recalculates as you type.

DNS Lookup

A, AAAA, MX, TXT and NS records with their TTLs, and who the domain is registered to: pulled live over DNS-over-HTTPS and RDAP.

Open DNS Lookup
whois + dnslive RDAP + DNS

Try any domain: live records and registration data.

MAC / OUI Lookup

The first half of every MAC address names the company that made the hardware. Paste one and see who: handy for an unfamiliar device on your LAN.

Open MAC / OUI Lookup
oui.lookuplive IEEE registry

Paste any MAC: live vendor lookup, with an offline fallback.

ASN Lookup

Every IP address belongs to an autonomous system. Look up who operates one, where it is registered, and what address space it announces.

Open ASN Lookup
asn.lookuplive RDAP

Try AS15169 (Google) or AS8075 (Microsoft): live registry data.

And 13 more, each on its own page:

Exam map

Studying for an exam? Here is where each part is taught

The official domains and weights for the two entry-level networking exams, mapped onto the tracks. A map to study from, not a promise that these lessons alone will pass you.

Cisco CCNA 200-301 v1.1

  • 120 minutes
  • US$300
  • Multiple choice, drag-and-drop and performance-based

Source: Cisco’s exam page

  1. Network Fundamentals20%

    Taught in FundamentalsAddressingSwitching

  2. Network Access20%

    Taught in SwitchingCisco

  3. IP Connectivity25%

    Taught in RoutingCisco

  4. IP Services10%

    Taught in Network servicesAddressing

  5. Security Fundamentals15%

    Taught in SecurityCisco

  6. Automation and Programmability10%

    Not covered here yet

CompTIA Network+ N10-009 (V9)

  • 90 minutes
  • Up to 90 questions
  • Pass mark 720 of 900

Source: CompTIA’s exam page

  1. Networking concepts23%

    Taught in FundamentalsAddressing

  2. Network implementation20%

    Taught in SwitchingRouting

  3. Network operations19%

    Taught in Network servicesTools & analysis

  4. Network security14%

    Taught in Security

  5. Network troubleshooting24%

    Taught in Tools & analysisCisco

Weights copied from each exam owner’s page, last checked 27 Sep 2026.

Blog

How it works, and how to fix it

Longer reads for people learning the fundamentals: explainers, troubleshooting walkthroughs and study plans.

All articles

Ready when you are

Your first packet is waiting.

Lesson one assumes nothing. No account, no email, nothing to install: open it and start.

Start lesson one Take the level check