CIDR

How it is used

Usually said like the drink 'cider'. Engineers use CIDR notation everywhere: in firewall rules, routing tables and cloud network settings. The number after the slash shows how many bits belong to the network: a /24 has 256 addresses, a /30 has four.

Example sentences

1. Write the subnet in CIDR notation, for example 10.10.0.0/16, not with the full mask.

2. The cloud team asked for a /20 CIDR block for the new environment.

Common collocations

• CIDR notation
• CIDR block
• CIDR range
• prefix length

Related terms

• subnetA smaller network created by dividing a larger IP address range, so that groups of devices such as offices, departments or servers can be kept separate and managed more easily.
• subnet maskA number such as 255.255.255.0 that shows which part of an IPv4 address identifies the network and which part identifies the device; it can also be written as a prefix such as /24.
• IPv4Version 4 of the Internet Protocol, which uses 32-bit addresses written as four numbers from 0 to 255 separated by dots, such as 192.168.10.5; it allows about 4.3 billion addresses.
• IP addressA unique numerical label given to every device on an IP network so that data can be sent to it, for example 192.168.1.20 in IPv4.
• routing tableA list stored in a router or host that shows which networks it knows about and where to send packets for each one, such as the next router or an outgoing interface.

This word in other fields

The same English word can have a different meaning in another field:

• CIDR · Software Engineering

More terms: IP Addressing

• default gateway
• IPv6
• NAT
• static IP address
• port forwarding
• private IP address