A network is a set of machines wired so they can pass data to each other. The point that trips people up: when does traffic go out to the internet, and when does it stay inside the house? Send some and watch the path.
Try it · send traffic and watch where it goesEvery device on a network gets an IP address: a number that says where it is. An address has two parts, a network part shared by everything on the same network, and a host part unique to each device. The prefix (the /24) marks where the split falls.
People remember names; machines route by numbers. DNS is the lookup that turns a name into an IP address. Look one up and watch the resolver walk the chain. The steps are how real resolution works; the addresses are examples.
Try it · look up a namenode.local never leaves your network. A known tracker is refused by your own resolver. Try all three.One machine runs many services, so each listens on a numbered door called a port. A door is only reachable when two gates are open: a service is listening behind it, and the firewall lets the connection through. Flip the gates and watch what an outsider can reach.
Try it · toggle the two gates on each portThis is what default-deny means: the firewall gate starts closed on every port, so a service is never exposed just because it is running. You open a gate only for what you need, only toward yourself.
Not needed to build the node. This is the layer underneath: how the pieces are modeled, what a packet carries, how addresses are carved up, and how networks are shaped.
Two models describe the same journey. The 7-layer OSI model is the teaching reference; the 4-layer TCP/IP model is what the internet actually runs. They map onto each other.
| OSI layer | TCP/IP | Does | Example |
|---|---|---|---|
| 7 Application | Application | The app's own data and rules | HTTP, DNS, SSH |
| 6 Presentation | Encoding and encryption | TLS | |
| 5 Session | Keeps a conversation open | sockets | |
| 4 Transport | Transport | Splits into segments, ports, reliability | TCP, UDP |
| 3 Network | Internet | Addresses and routes packets | IP, ICMP |
| 2 Data Link | Link | Frames between adjacent devices | Ethernet, MAC |
| 1 Physical | The wire or radio itself | cabling, wifi |
Your data does not travel alone. Each layer wraps it in a header, like nested envelopes. Click a segment to see what it carries.
A prefix splits an address block into a network and the hosts inside it. Enter an address and prefix to see the real numbers.
Usable hosts = 2^(32 − prefix) − 2 (the network and broadcast addresses are reserved). A /24 gives 254; a /30 point-to-point link gives 2.
How the machines are wired together. Your build uses a star.
Every device connects to one central point, your switch and router. Simple, and the standard for a home or small network.
Devices connect to many others, so traffic has more than one path. Resilient, but more wiring and overhead.
All devices share one line. Cheap and old; one break can take down the segment.
Each device links to two neighbors in a loop. Used in some backbones; a break is routed around.