# Difference between revisions of "Networking: some CIDR calculations"

## How to convert a number to a binary number

In the networking IP4 calculations, an IP address is composed of 32 bits, divided into 4 octets: 00000000.00000000.00000000.00000000 The binary numbers available per octet are: 128 - 64 -32 -16-8- 4 -2-1

How to translate a number to a binary number? 192.168.1.0
128 - 64 -32 -16-8- 4 -2-1
192 = 128 + 64 = 11000000
168 = 128 + 32 + 8 = 10101000
1 = 00000001
0 = 00000000
192.168.1.0 = 11000000.10101000.00000001.00000000

## Example 1 CIDR block 172.16.0.0/12

1. What is the subnet mask? the first 12 bits are used (/12), which are all ones. the remaining bits are all zeros.
11111111.11110000.00000000.00000000 => 255.240.0.0

2. What is the network identifier?
First translate the IP address in a binary number: (Use 128-64-32-16-8-4-2-1 to help calculate)
10101100.00010000.00000000.00000000
The network part is formed by the first 12 bits.
This corresponds to 10101100.0001

3 Number of available hosts?
2(32-12) – 3 = 1048573

3. What is the first and the last IP address available?