IP addresses and subnets

93.184.216.34 (IPv4) or 2606:2800:220:1:248:1893:25c8:1946 (IPv6) is a numeric address that routers use to forward packets toward it — conceptually closer to a postal address than to a name. The same physical machine can have different IP addresses over time (your laptop gets a new one on every Wi-Fi network), and one IP address can represent thousands of different machines sitting behind it (a load balancer, a NAT gateway — both covered later in this domain).

IPv4 addresses are 32 bits, written as four dot-separated numbers 0–255 (192.168.1.1). There are only about 4.3 billion possible IPv4 addresses — long since exhausted for direct public assignment, which is the entire reason the private/public split below exists, and why IPv6 (128 bits, room for roughly 340 undecillion addresses) exists at all.

Three specific ranges are reserved as private — routable within a local network, but every router on the public internet is configured to silently drop packets addressed to them:

Your home router almost certainly hands out 192.168.1.x addresses to every device on your Wi-Fi. All of them share ONE public IP address (your router's), which is why this works at internet scale despite only ~4.3 billion IPv4 addresses existing for billions of devices — most devices never need a public address at all, only a path to something that has one (your router, doing NAT — covered in a later lesson).

192.168.1.0/24 means "the first 24 bits are fixed (the network), the remaining 8 bits vary (the hosts)" — a range of 256 addresses, 192.168.1.0 through 192.168.1.255. The /24 is the subnet mask length. Smaller numbers after the slash mean a bigger range: /16 covers 65,536 addresses, /8 covers over 16 million.

This is the exact notation you'll type into every cloud provider's VPC/subnet setup — AWS, GCP, and Azure all use CIDR blocks to define network boundaries, and misreading a /24 as "24 addresses" instead of "24 fixed bits" is a genuinely common early mistake.

A cloud VPC (Virtual Private Cloud) typically gets one large CIDR block — 10.0.0.0/16, say — then gets split into smaller subnets for different purposes: a /24 for public-facing servers, another /24 for a private database tier that has no direct internet route at all. Splitting this way means a security rule ("nothing from the internet reaches the database subnet directly") can be enforced at the network level, not just hoped for in application code.

IPv6 addresses are written as eight groups of hex digits (2606:2800:220:1:248:1893:25c8:1946), with :: allowed once per address to compress a run of zero groups. The private/public split still conceptually exists (IPv6 has its own "unique local" range, fc00::/7), but IPv6's address space is so large that NAT is no longer a practical necessity the way it is for IPv4 — every device can plausibly get its own globally unique address. Most production systems today still run dual-stack (both IPv4 and IPv6 simultaneously) rather than IPv6-only, since not every network path supports IPv6 yet.