routing.jelia.nyc is our new deep dive into routing: the machinery inside a router that forwards every packet, and the protocols inside and between networks that decide where those packets go.
It picks up where networks.jelia.nyc stops. That site teaches routing tables and the basics of OSPF and BGP; this one opens the box. It runs to fifteen chapters, a history and a glossary of 192 terms, written so a curious owner and a working network engineer can both get something from it. Every chapter has a narrated walkthrough and live instruments you can drive, and break, safely.
What it covers
- Inside a router: control plane and data plane, RIB and FIB, and longest-prefix lookup at line rate with tries and TCAM
- Interior routing: distance vector and counting to infinity, OSPF in depth, IS-IS, and fast reroute with BFD and loop-free alternates
- BGP and the internet: sessions and messages byte by byte, who pays whom, transit, peering and exchange points
- Keeping it honest: how hijacks and route leaks happen, and how RPKI, route origin validation and ASPA catch them
- Engineered paths and practice: MPLS and segment routing, multicast, data-center fabrics, and the public tools for watching the routing system
How it is built
- Every instrument is a real computation running in your browser: Bellman-Ford rounds, Dijkstra, a trie you can walk, ECMP hashing, ROA validation, a BGP state machine
- Every fact is checked against its source, mostly the RFCs themselves, and every chapter lists them
- Large type, high contrast, dark mode and a color-blind friendly palette throughout
It is the same knowledge we rely on every day running mail, sign-on and web services for our clients. When a site is unreachable from one network and fine from another, the answer is almost always somewhere in these chapters.
Read it: routing.jelia.nyc. Start with how a router forwards a packet.