What is an IPv4 address and what are its key components?

A 32-bit address in dotted-decimal notation (four 0-255 numbers) used to locate devices; full communication also needs a subnet mask and a default gateway.

An IPv4 (Internet Protocol version 4) address is how a device is found on a network — it's the "where to deliver" label on every packet, the primary means for devices to locate one another and communicate end-to-end. The 32 bits are split into four 8-bit groups and written in dotted-decimal notation: four numbers from 0 to 255 separated by periods, e.g. 192.168.1.10 (8 bits can only count to 255, which is why no group ever exceeds it).

But an address alone isn't enough to talk on a real network — three settings work together:

• IP address — the device's own unique identifier
• Subnet mask (e.g. 255.255.255.0) — tells the device which part of the address is the network and which is the host, so it knows whether a destination is local or remote
• Default gateway — the IP of the local router; the device sends anything destined for another network here, so without it the device can't reach the internet

Go deeper:

• IPv4 (Wikipedia) — the 32-bit address space and dot-decimal notation in detail.
• Default gateway (Wikipedia) — the third setting that lets a host reach other networks.