Reading CIDR Slash Notation
Learn how /24 and similar notations describe a subnet quickly.
What CIDR Means
CIDR stands for Classless Inter-Domain Routing. It replaced rigid address classes with flexible masks of any length, written using slash notation like /24.
The number after the slash is simply the count of 1 bits in the subnet mask — that is, how many bits belong to the network portion.
The Slash Is a Bit Count
In 192.168.1.0/24, the /24 means the first 24 bits are network. Since 24 bits fill the first three octets, the mask equals 255.255.255.0.
The remaining 8 bits are for hosts. The slash format is shorter and clearer than writing the full dotted-decimal mask.
/24 = 255.255.255.0
/16 = 255.255.0.0
/8 = 255.0.0.0All lessons in this course
- What a Subnet Mask Does
- Reading CIDR Slash Notation
- Counting Hosts in a Subnet
- Splitting a Network Into Subnets