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Glossary Networking

CIDR

CIDR (Classless Inter-Domain Routing) is the notation that writes an IP network as an address plus a prefix length, such as 192.168.1.0/24.

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In more detail

The prefix length says how many leading bits identify the network, so a /24 leaves 8 bits (256 addresses) for hosts. CIDR replaced the old fixed A, B and C address classes and lets blocks of any power-of-two size be allocated and combined (route aggregation).

Try these tools

CIDR to IP Range Converter

Convert a CIDR block (e.g.

IP Range to CIDR Converter

Convert a first-last IP address range into the minimal set of covering CIDR blocks.

CIDR Aggregator

Merge a list of CIDR blocks into the minimal set of covering supernets.

See also

  • Glossary Subnet mask
    A subnet mask is a 32-bit value that marks which part of an IPv4 address identifies the network and which part identifies the host.
  • Cheat sheet CIDR and Subnet Mask Cheat Sheet
    Every IPv4 prefix from /8 to /32 with its subnet mask, wildcard mask, address count and usable hosts.
  • Guide How Subnetting Works
    How an IP address splits into network and host parts, how to find a network and broadcast address.
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