What is Actually Inside a Network: Firewalls, Load Balancers, and the Internet Hierarchy
Networking from Scratch (lesson 10) — the middleboxes a packet traverses on the way to a real-world server (firewalls, load balancers, proxies, IDS/IPS, WAFs, VPN gateways), what each one does and where it sits, plus the internet hierarchy from IANA through RIRs and ISP tiers to IXPs and CDNs.