CIDR
n.n. Stands for Classless Inter-Domain Routing. A way for computers on the internet to share IP addresses more efficiently by grouping them together.
n. Abbreviation for Classless Inter-Domain Routing. A method for allocating IP addresses and routing Internet Protocol packets that replaces the older system based on fixed classes (A, B, and C).
The network administrator assigned a new CIDR block to the office.
Using CIDR notation allows engineers to define a range of IP addresses with a single prefix and a slash.
The introduction of CIDR in 1993 was essential for slowing the exhaustion of IPv4 addresses and preventing the explosion of routing tables across the global internet backbone.
An initialism for Classless Inter-Domain Routing, the term was coined in 1993 to denote a departure from the previous system of network classification.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Often used as a modifier before nouns like 'block', 'notation', or 'address'.
Last updated July 22, 2026