Add network & containerisation

Doc/Network/Basics.md

@@ -1,16 +1,119 @@
 # Network – Basics
 
-This page is for general networking concepts I reuse across projects.
+Core networking concepts: IP addressing, subnets, ports, routing, and protocols.
 
-At the end of each topic, I link to my home server implementation when it exists.
-
-Related detailed pages:
+Related pages:
 
 - [Network / DNS](./DNS.md)
-- [Network / VPN Basics](./VPN/Basics.md)
 - [Network / Reverse Proxy](./ReverseProxy.md)
+- [Network / SSH](./SSH.md)
+- [Network / VPN Basics](./VPN/Basics.md)
+- [Network / Firewall](./Firewall.md)
 
-## TODO
+---
 
-- Add sections for IP addressing, routing, DNS, and HTTP(S).
-- Link to home-server implementation pages from each section.
+## 1. IP Addresses
+
+Every device on a network is identified by an **IP address**. The most common version is IPv4, written as four numbers separated by dots: `192.168.1.18`. Each number is between 0 and 255, giving 4 bytes (32 bits) per address.
+
+### 1.1 Private vs Public Addresses
+
+Some ranges are reserved for private use — they are only valid inside a local network and are never routed on the public internet:
+
+| Range             | Example         | Common use                   |
+|-------------------|-----------------|------------------------------|
+| `10.0.0.0/8`      | `10.10.10.1`    | VPNs, corporate networks     |
+| `172.16.0.0/12`   | `172.16.0.1`    | Docker default bridge        |
+| `192.168.0.0/16`  | `192.168.1.18`  | Home/office LANs             |
+
+Everything else is a **public** address, routable on the internet. Your internet box has one public IP assigned by your ISP.
+
+### 1.2 Subnets and CIDR Notation
+
+A subnet groups a range of IP addresses together. The size is expressed with **CIDR notation**: a `/` followed by the number of fixed bits.
+
+- `/24` → first 24 bits are fixed → 256 addresses (`192.168.1.0` to `192.168.1.255`).
+- `/32` → all 32 bits are fixed → exactly one address.
+- `/16` → first 16 bits are fixed → 65 536 addresses.
+
+The most common home network is a `/24`, for example `192.168.1.0/24`.
+
+A **subnet mask** expresses the same thing differently: `/24` ↔ `255.255.255.0`.
+
+---
+
+## 2. Ports
+
+An IP address identifies a machine. A **port** identifies a specific service or application running on that machine. Ports are numbers from 0 to 65 535.
+
+When two machines communicate they use an IP + port pair: `192.168.1.18:80`.
+
+### 2.1 Why Ports Exist
+
+A server typically runs several services at once — a web server, an SSH daemon, a database, etc. Ports allow the OS to route each incoming packet to the correct service.
+
+- A packet arrives at `192.168.1.18:443` → the OS delivers it to the HTTPS server.
+- A packet arrives at `192.168.1.18:22` → the OS delivers it to the SSH daemon.
+
+When you "open a port", you are telling a firewall or router to allow traffic destined for that port number to pass through.
+
+### 2.2 TCP vs UDP
+
+| Protocol | Characteristics                                              | Common uses                               |
+|----------|--------------------------------------------------------------|-------------------------------------------|
+| **TCP**  | Connection-oriented, reliable, ordered delivery             | HTTP/HTTPS, SSH, databases, email         |
+| **UDP**  | Connectionless, no delivery guarantee, lower overhead       | DNS, WireGuard, video streaming, QUIC     |
+
+TCP establishes a connection before transferring data and retransmits lost packets. UDP fires packets without verifying receipt — faster but not guaranteed.
+
+### 2.3 Well-Known Ports
+
+Ports 0–1023 are "well-known" — standardised assignments used by common services:
+
+| Port  | Protocol | Service                  |
+|-------|----------|--------------------------|
+| 22    | TCP      | SSH                      |
+| 53    | TCP/UDP  | DNS                      |
+| 80    | TCP      | HTTP                     |
+| 443   | TCP      | HTTPS                    |
+| 51820 | UDP      | WireGuard (conventional) |
+
+Ports 1024–49 151 are "registered". Ports 49 152–65 535 are "dynamic" (used temporarily for outbound connections).
+
+For filtering and controlling port access, see [Network / Firewall](./Firewall.md).
+
+---
+
+## 3. Routing
+
+Routing is the process of forwarding packets from one network to another. At home this is mostly transparent:
+
+1. Your device sends a packet.
+2. If the destination is on the same subnet, it is delivered directly.
+3. Otherwise it is sent to the **default gateway** (your router), which forwards it towards the internet.
+
+The default gateway is normally the IP of your router on the local network (for example `192.168.1.1`).
+
+---
+
+## 4. HTTP and HTTPS
+
+**HTTP** (HyperText Transfer Protocol) is the protocol used by web browsers and APIs. It is a request-response protocol over TCP:
+
+- A client sends a request: `GET /page HTTP/1.1`
+- A server responds with a status code and a body: `200 OK`
+
+**HTTPS** is HTTP over a **TLS** (Transport Layer Security) encrypted connection. TLS:
+
+- Encrypts traffic so it cannot be read in transit.
+- Authenticates the server via a certificate.
+
+Modern browsers require HTTPS. Self-signed certificates work for internal networks but require the client to explicitly trust the issuing CA.
+
+For TLS and certificates in depth, see:
+
+- [Security / Certificates](../Security/Certificates.md)
+
+For HTTP routing via a reverse proxy, see:
+
+- [Network / Reverse Proxy](./ReverseProxy.md)