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CIDR, short for Classless Inter-Domain Routing, is a way to write an IP address or a whole IP range in one short form, like 192.168.0.0/24. The number after the slash says how many bits identify the network, which sets the size of the range. It works for both IPv4 and IPv6.
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.
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 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::/32
When working with CIDR notation, we recommend using tools available online:
These tools will help you switch back and forth between human-readable IP format and machine-readable CIDR format.
ClickGuard fully supports blocking IP addresses and ranges using the CIDR format. This makes it possible to perform very specific IP range blocks (e.g. preventing an entire ISP's network from seeing ads by blocking out all their assigned CIDR ranges).
See also: What are IPs and IP ranges.