CIDR stands for Classless Inter-Domain Routing. It is a set of Internet protocol standards that is used to create unique identifiers for networks and individual devices. Basically, CIDR notation is used to represent individual IP addresses or IP ranges.

CIDR is used for both IPv4 and IPv6 addresses and ranges.

A CIDR IP addresses consist of two groups of numbers (bits). The primary bit group is the network address, and it is used to identify a network or a sub-network (subnet). The secondary bit group is the host identifier.

CIDR examples

CIDR representing a single IPv4 address 192.168.10.50:

192.168.10.50/32

CIDR representing an IPv4 address range 192.168.10.0 - 192.168.10.255:

192.168.10.0/24

CIDR representing an IPv4 address range 192.168.0.0 - 192.168.255.255:

192.168.0.0/16

CIDR representing an IPv6 address range 2001:4860:4860:0000:0000:0000:0000:8888 - 2001:4860:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:

2001:4860:4860::8888/32

CIDR Tools

When working with CIDR notation, we recommend using tools available online:

These tools will help you switch back and fourth between human readable IP format and machine readable CIDR format.

How does ClickGUARD use CIDR format?

ClickGUARD fully supports blocking IP addresses and ranges using CIDR format. This makes it possible to perform very specific IP range blocks (e.g. preventing an entire ISPs network from seeing ads by blocking out all their assigned CIDR ranges).

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