CIDR and Subnets Explained for Beginners

Quick answer: CIDR notation describes how many bits of an IP address identify the network. For example, 192.168.1.0/24 represents a common IPv4 subnet size.

What the slash means

The number after the slash is the prefix length. A larger prefix leaves fewer host addresses; a smaller prefix covers a larger address block. Network engineers use CIDR to allocate address space efficiently and to summarize routes.

Why this appears in IP tools

ASN, WHOIS/RDAP and routing data often describe IP ranges rather than individual addresses. Understanding CIDR makes those results much easier to read.

You can use WHOIS Lookup or ASN Lookup to inspect network ownership data.