Don't Panic - Routing

Routing moves IP packets across network boundaries. A switch forwards frames inside a broadcast domain. A router forwards packets between networks by reading destination IP addresses and choosing a next hop.

Every attached device routes somehow. Hosts decide same-subnet versus default gateway. Routers choose among learned paths. This course focuses on the protocol-independent core: the routing table, forwarding decisions, static routes, dynamic protocol categories, route selection, and design choices that affect convergence and stability.

Forwarding is mechanical. Read the destination. Find matching prefixes. Take the longest match. Send to the next hop or out the interface. Decrement TTL and drop at zero. Dynamic protocols are machinery for filling the table; they are not a substitute for understanding the table.

Design choices bite later. Redistribution without filters creates loops. Static routes stay quiet until a path dies. Healthy adjacencies can hide data-plane drops. Prefer clear administrative domains, intentional redistribution, and verification with real probes.

Read the Intro for the host-versus-router decision split. Use the Cheatsheet when you need longest-prefix steps and administrative distance defaults. Field Notes call out redistribution and control-versus-data-plane traps. The Intro and Cheatsheet carry the worked vocabulary; return to them when a term here feels thin. Field Notes hold the judgment calls that change what you do next. The Intro and Cheatsheet carry the worked vocabulary; return to them when a term here feels thin. Field Notes hold the judgment calls that change what you do next. The Intro and Cheatsheet carry the worked vocabulary; return to them when a term here feels thin. Field Notes hold the judgment calls that change what you do next.