How a network works: packets, addresses and neighbours
What actually travels between two machines, and how each one decides whether the destination is a neighbour or somebody else's problem.
The networking course teaches you to diagnose "unreachable". This one teaches what was reachable in the first place. A machine does not send a file: it sends thousands of individually addressed packets, and for every one of them it asks the same question again — is this destination on my own network, or do I hand it to somebody else? The prefix is what answers, and this course explains how.
What you will be able to do
- Explain what actually crosses the wire, and why a file never goes over it whole
- Work out a prefix's network address, broadcast address and host count by hand, including a /26
- Say whether two addresses are on the same network — and what the machine does in each case
- Read the neighbour table and explain what a MAC address is doing in it
- Follow a packet from router to router, and say why a star in a traceroute proves nothing
Before this course
Taken from the learning path this course belongs to: the course placed just before it. A suggested order, not a lock — nothing here closes until you have finished it.
Outline
- 01
What actually travels
Packets, not a stream: what each layer adds, what the prefix decides, and how a machine finds its neighbour.
- 02
Beyond your own link
What becomes of a packet once it is handed to the gateway: successive hops, the addresses that ran out, and the second address family.
Technical content last reviewed on 20 September 2026