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Learning path · 5 parts

The Internet in Practice

The everyday operation of the network — how a device joins it, the applications and architectures built across it, how to see inside it, and how it is defended.

About 1 hour of reading · 10 widgets

Start with DHCP: How Your Device Joins a Network
  1. Networks & the Internet9 min

    Part 1: DHCP: How Your Device Joins a Network

    How a device with no address at all joins a network: the DORA handshake that leases it an IP address, subnet mask, default gateway, and DNS server automatically — on a lease that quietly expires.

  2. Networks & the Internet10 min

    Part 2: Email: The Internet's Oldest Application

    Email is a distinct application on the internet's plumbing, older than the web. It relays store-and-forward from mail server to mail server via a DNS MX lookup, and by original design never checked who the sender claimed to be — which is why SPF, DKIM, and DMARC exist.

  3. Networks & the Internet10 min

    Part 3: Peer-to-Peer: The Internet Without a Center

    In a peer-to-peer network there is no central server — every node is both client and server. BitTorrent splits a file into pieces and a swarm trades them, so the more people want a file, the faster everyone gets it.

  4. Networks & the Internet9 min

    Part 4: Ping and Traceroute: Seeing the Network

    Ping times an echo to tell you a host is alive and how far away it feels; traceroute lists every router in between by deliberately expiring packets one hop farther each time. Both ride on ICMP.

  5. Networks & the Internet9 min

    Part 5: Firewalls: Filtering the Traffic

    A firewall decides which traffic may pass by matching packets against rules on address, port, and protocol. The real leap is memory: a stateful firewall welcomes the replies to connections you started while turning away strangers who arrive uninvited.