Routing fundamentals
From your first static route to BGP policy at the edge, in the order the skills build.
Addresses come first. If you can carve a network on paper, every routing decision after this makes sense.
One missing route between two hosts. The routing table itself is the lesson.
Most networks reach the world through one exit. Point the branch at it.
Routing is hop by hop. Fix the path one router at a time and watch where packets die.
A backup route that stays quiet until the primary fails teaches administrative distance.
Hand-written routes stop scaling. Bring up your first OSPF adjacency and let the routers talk.
The protocol picks the path. Steer it with interface cost instead of fighting it.
Between organizations the rules change. Bring up an eBGP session and read its state machine.
Real edges filter what they accept. Write policy, not just configuration.
Two upstreams, and you pick the path each way. Prefer one outbound and steer inbound to match.