IPv4 Addressing

Learning objective

Read an IPv4 address and prefix, separate its network and host portions, and recognize addresses that have special local purposes.

Read an IPv4 address

IPv4 identifies an interface with 32 bits. People normally write those bits as four octets, such as 192.0.2.44. Each octet contains eight bits and therefore ranges from 0 to 255. An address identifies a logical attachment to an IP network; it is not a permanent identity for the whole device.

Dotted decimal and binary

The positions in one octet have values 128, 64, 32, 16, 8, 4, 2, 1. Add the positions whose bits are 1. For example, 11000000 is 128 + 64, or 192. Dotted decimal is only a readable representation of the same binary value routers process.

Interactive binary explorer

Build one IPv4 octet

Each switch represents one binary place value. Toggle it and watch the decimal octet change.

128164132016080402010

192 = 11000000

Prefixes, network and host portions

The prefix length tells you how many leading bits form the network portion. The remaining bits form the host portion. In 192.0.2.44/24, the first 24 bits identify 192.0.2.0/24; the last eight select an address inside it. A prefix is not optional decoration—it changes the boundary.

Interactive address boundary

Reveal the network boundary

Choose an address scenario

Documentation examplePrivate office hostLink-local fallback

192.0.2.44/24

Network: 192.0.2.0Broadcast: 192.0.2.255Network bits: 24Host bits: 8Type: documentation

Special address ranges

Not every syntactically valid address is a normal internet destination. Private ranges are commonly used inside organizations and are not globally routed by default. 127.0.0.0/8 is loopback for the local host. 169.254.0.0/16 is IPv4 link-local, often indicating that normal configuration failed. The documentation ranges 192.0.2.0/24, 198.51.100.0/24, and 203.0.113.0/24 are safe for examples. Public addresses are not automatically reachable, owned by you, or safe to expose.