CIDR

CIDR stands for Classless Inter-Domain Routing, which is an IP addressing method used to allocate IP addresses efficiently and route internet traffic. 10.0.0.0 is a simple 32-bit number, and by reading this number, a router does not know the name of a network. However, 10.0.0.0/8 expresses a range of IP addresses, which tells a router how large that specific network is. The / symbol we see, along with the number following it, is called CIDR notation. The CIDR notation indicates how many bits are locked in a 32-bit IP address starting from the left. These locked bits represent the Network ID (building), while the remaining unlocked bits represent the Host IDs (specific systems).

Conclusion

Originally, IP addresses were provided in CLASSES (Class A, Class B, and Class C), and every class had a specified amount of IPs. As a result, you received a massive block of addresses whether you needed that many or not, which meant there was no in‑between option to choose. This led to the huge wastage of many IPs. Then came CIDR, which served as the hotfix, and subnetting became the practical application of that fix.

IP Subnetting

Subnetting is the process of taking large block of IP addresses and mathematically slicing it into smaller networks (subnets) according to the ammount of IP addresses needed from a particular RFC 1918 CLASS.

Subnet Masking

Subnet Masking is the specific tool used to define those subnets. Here we actually freeze some parts (eg. /8) of an 32-bit IP from the left and the rest of the parts can still be changed to get unique IPs.

IP Subnetting with MXToolbox

• Open this website in a new tab MXToolbox
• Provide a RFC 1918 Private IP eg. 10.0.0.0

• Click on dropdown menu

• According to how much IPs you need select CIDR suffix for that like I want 16 of it

• You will see the output details

Creating separate networks out of single network (splitting subnet into subnets)

• suppose to divide a network into two networks having equal ammount of IPs eg. 10.0.0.0/16 into two 256 IPs
• first network we choose 10.0.0.0/24

• second network we choose 10.0.1.0/24

• we can choose 255 networks like this eg. 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24 ..., and each network consists of 255 IPs.