What happens in the first seconds after a device connects to a network, from getting an IPv4 address with DHCP and finding neighbors with ARP to configuring IPv6 with router advertisements, SLAAC, Neighbor Discovery and DHCPv6.
How the Domain Name System turns names like www.example.com into IP addresses, from the tree of domain names and the servers that hold them to caching, record types, message formats and security.
How an email travels from one inbox to another, from the SMTP conversation between servers and the difference between envelope and header to MIME, mailbox access, and the SPF, DKIM and DMARC checks that fight forgery.
How the Hypertext Transfer Protocol carries the web, from URLs, requests, methods and status codes to caching, cookies and the three versions in use today, HTTP/1.1, HTTP/2 and HTTP/3.
How the independent networks of the internet find paths to each other with the Border Gateway Protocol, from autonomous systems and AS paths to route selection, business relationships, route hijacks and leaks, and RPKI.
What an IP address identifies, how IPv4 and IPv6 addresses are written and divided into networks, which ranges are reserved, and how a packet travels from one address to another.
How network address translation lets many devices share one public IPv4 address, how NATs map and filter traffic, and how STUN, TURN and ICE still connect two devices that are both behind one.
How computers keep their clocks right with the Network Time Protocol, from the hierarchy of time servers and the four timestamps of each exchange to choosing between servers, adjusting the clock, leap seconds, the year 2036 and Network Time Security.
How QUIC, the transport protocol under HTTP/3, combines the jobs of TCP and TLS on top of UDP, from its packets, connection IDs and streams to its one-round-trip handshake, loss recovery and connection migration.
How the Transmission Control Protocol turns unreliable packets into a reliable stream of bytes, from ports and the three-way handshake to acknowledgments, retransmission, flow control and congestion control.
How Transport Layer Security protects data on the internet, from the cryptographic building blocks and the TLS 1.3 handshake to certificates, the key schedule, resumption and what TLS cannot hide.
How WebSockets give a web page a lasting two-way connection to a server, from the HTTP upgrade that opens it to frames, masking, pings and the closing handshake, and how they run over HTTP/2 and HTTP/3.