What Is a Network?
A network is a system that connects computers so they can exchange data. Think of it as a road system: computers are cities, and the network is the roads connecting them. Data travels along these roads in small envelopes called packets.
IP Addresses: Like Street Addresses
Every device on a network has an IP address — a numerical label that identifies it, much like a street address identifies a house.
- IPv4: Four numbers separated by dots, e.g.,
192.168.1.1. This gives about 4 billion unique addresses — not enough for the whole world. - IPv6: Eight groups of hex digits separated by colons, e.g.,
2001:0db8:85a3::8a2e:0370:7334. This gives 340 undecillion addresses — enough for every device on Earth.
Ports: Like Apartment Numbers
A single computer can run many services at once — a web server, an email server, a file server. Ports distinguish these services, like apartment numbers in a building.
| Port | Service |
|---|---|
| 80 | HTTP (web) |
| 443 | HTTPS (secure web) |
| 25 | SMTP (email) |
| 22 | SSH (secure shell) |
| 53 | DNS (name resolution) |
Ports 0–1023 are well-known ports. Ports 1024–49151 are registered. Ports 49152–65535 are ephemeral (temporary, used by your computer for outbound connections).
Packets: Envelopes Carrying Data
When you request a web page, the data doesn't travel as one blob. It's split into packets — small envelopes that each carry a piece of the data along with addressing information. Each packet has:
- Payload — the actual data being sent
- Header — source and destination IP addresses, port numbers, and error-checking data
- Sequence number — so the receiver can reassemble packets in the correct order
Client-Server vs. Peer-to-Peer
The client-server model is the most common: a client asks a server for something, and the server responds. Your browser is the client; websites run on servers.
Peer-to-peer (P2P) is an alternative where every participant is both client and server. BitTorrent uses this model to share files.
Next Steps
Now that you understand the basic vocabulary, you can trace what happens when a packet travels through the network. See Trace a Packet Through Network Layers.
This article begins the Networking From the Ground Up learning path.