CIDR Notation Explained (e.g., 203.0.113.0/24)

CIDR is a notation for IP ranges like 203.0.113.0/24. It helps describe how IP address blocks are allocated and routed.

What does /24 mean?

The /24 is a prefix length: it means the first 24 bits are the network portion. The remaining bits represent addresses inside that network.

CIDR and subnet masks

CIDR prefix lengths are another way to express subnet masks. For example, /24 corresponds to 255.255.255.0 and/16 corresponds to 255.255.0.0. This makes ranges easier to read in routing, firewall, and ISP allocation contexts.

Quick mental examples

• 10.0.0.0/8: very large private range used in internal networks
• 192.168.1.0/24: common home-network style segment
• 203.0.113.0/24: documentation example block

Why CIDR shows up in IP tools

• IP ranges are allocated to ISPs and organizations in CIDR blocks
• Routing announcements (BGP) advertise prefixes
• Security teams use CIDR to block/allow ranges

Related glossary terms: CIDR, ASN, and NAT.

To see the network details for a public IP, use the IP Address Lookup.