The author describes how their custom traceroute program, ktr, works by sending Internet Control Message Protocol (ICMP) packets to trace the path taken by data packets across the Internet. Each packet has a Time to Live (TTL) value that decreases with each hop between routers. When the TTL reaches zero, the router sends an error message back, revealing its IP address. By sending packets with increasing TTL values, the program builds a list of routers encountered along the path to a destination. The article details the technical aspects of the website's loading mechanism. The server sends the initial web page response while simultaneously running the traceroute. It updates the web page in real-time without JavaScript, using CSS to hide previous iterations of the traceroute display. The author admits to a slight inaccuracy: the traceroute reflects the path from their server to the user’s computer, effectively a reverse traceroute, which could differ from the actual route taken. The piece explains the concept of autonomous systems (AS) — networks of routers owned by companies that decide how to connect with each other. Each AS is assigned an Autonomous System Number (ASN) for identification. The author emphasizes that the Internet is not as decentralized as it seems; it consists primarily of corporate networks. They also touch on the WHOIS protocol, which provides information about IP addresses and ASNs, and the challenges of parsing its varied response structures. Finally, the author briefly introduces the Border Gateway Protocol (BGP), which governs how packets are routed between different networks.