Your free access ends in 7 days — and you haven’t tried it yet. Watch one algorithm run, start to finish. It takes about two minutes.

Try one problem

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.

InIntroduction to NetworkingWhy networks matter to developers — and the road ahead · 12 sections

Part A · Fundamentals

IP, MAC, subnets, gateways & ARP — the base layer.

  1. 01How an HTTP Request TravelsFrom fetch() in your code to bits on the wire — the full encapsulation journey · 12 sections
  2. 02The Structure of an IP AddressOctets, dotted-quad notation, and why IPv4 is exactly 32 bits · 6 sections
  3. 03Network, Host & CIDRSplitting an IP into a network part and a host part — and writing it as /24 · 9 sections
  4. 04The Subnet MaskHow a device uses a mask and a bitwise AND to decide: send direct, or route? · 9 sections
  5. 05The Default GatewayThe device your packets go to when the destination is not on your network · 6 sections
  6. 06Putting It TogetherHow a router bridges two networks — intra-network vs inter-network delivery · 7 sections
  7. 07The Structure of a MAC AddressThe permanent, physical, 48-bit address baked into every network interface · 8 sections
  8. 08MAC vs IPWhy we need two different addresses — and what each one is really for · 8 sections
  9. 09All About ARPHow a device turns an IP into a MAC — broadcast, reply, and cache · 9 sections

Part B · Protocols

Routing, ICMP, TCP/UDP, DNS, HTTP, TLS, DHCP & NAT.

  1. 10The TCP/IP & OSI ModelsThe layered map that organizes every protocol you have met so far · 7 sections
  2. 11How Routing Works (In Depth)Routing tables, hop-by-hop forwarding, and why the MAC changes but the IP does not · 7 sections
  3. 12ICMP: ping & tracerouteThe internet’s status-and-error protocol — and the tools you already use built on it · 7 sections
  4. 13UDP — The Fast ProtocolConnectionless, no guarantees, tiny overhead — and perfect for the right jobs · 6 sections
  5. 14Anatomy of a UDP DatagramThe whole UDP header is just four fields and eight bytes · 6 sections
  6. 15TCP — The Reliable BackboneConnection-oriented delivery, the 3-way handshake, and the graceful close · 7 sections
  7. 16TCP Sequence & Acknowledgement NumbersThe counters that make delivery reliable and in-order · 7 sections
  8. 17TCP Segment, MTU, MSS & FragmentationThe segment header, size limits on the wire, and what happens when data is too big · 7 sections
  9. 18TCP Flow ControlThe sliding window that stops a fast sender from drowning a slow receiver · 7 sections
  10. 19TCP Congestion ControlHow TCP avoids melting the network — slow start, AIMD, and ECN · 8 sections
  11. 20DNS — How Resolution WorksFrom a name to an IP by walking the root, TLD, and authoritative servers · 7 sections
  12. 21DNS Records & Email SecurityThe record types you will actually configure — and how they stop email spoofing · 8 sections
  13. 22HTTP & Its VersionsFrom HTTP/1.1 to HTTP/3 — how the web’s core protocol got faster · 7 sections
  14. 23WebSocketsA persistent, two-way channel for real-time apps · 6 sections
  15. 24TLS & HTTPSHow the padlock works: encryption, integrity, and proving who you are talking to · 6 sections
  16. 25DHCPHow your device gets an IP the instant it joins a network · 6 sections
  17. 26NATHow a whole household of devices shares one public IP address · 6 sections

Part C · Going Further

IPv6, ports, network devices, proxies/CDNs & Wireshark.

  1. 27IPv6The 128-bit successor to IPv4 — and why it barely needs NAT · 6 sections
  2. 28Ports & SocketsHow one machine runs many services — and what a "connection" really is · 6 sections
  3. 29Hubs, Switches & RoutersThe three devices that build networks — and how traffic is addressed to one, all, or a group · 6 sections
  4. 30Proxies, Load Balancers, CDNs & VPNsThe middle-boxes that make real-world apps fast, scalable, and private · 6 sections
  5. 31Seeing It Live — WiresharkWatch the theory of this course happen on a real wire · 6 sections

32 chapters · every concept illustrated.