IP Addresses and Subnets

An IP address is what lets a packet leave its own link and reach a machine on another network, and a prefix such as /24 decides which part of the address names the network. Reading those prefixes is everyday work: every cloud network, firewall rule and VPN is configured in them, and a mistake made when a network is first laid out is very hard to undo later.

The network layer's job comes first, then the parts of an IPv4 address and the steps that turn a prefix into a count of addresses. Two examples apply those steps, one deciding whether two addresses share a network and one dividing a cloud network into subnets. Private ranges and NAT, IPv6, and the overlapping ranges that stop two networks being joined complete the topic.

How a router uses these addresses to choose a path belongs to routing, the next topic.

By the end you can count the addresses in a block, decide whether two addresses share a subnet, and split a range into subnets that do not overlap.