Introduction

This is the contemporary IP addressing scheme, which completely does away with the separation between IP networks into classes. It is particularly flexible because it allows network blocks of arbitrary size, however, it does come with added complexity.

The premise behind CIDR is to do away with classes entirely and instead let the cusp between the network and host ID vary arbitrarily.

CIDR ("Slash") Notation

The dividing line between the Network and Host IDs is specified via the slash notation: x.x.x.x/y where the number after the slash specifies the number of bits that are used for the Network ID.