# How do you calculate CIDR subnet mask?

## How do you calculate CIDR subnet mask?

The process to determine the subnet mask for a CIDR address is straight forward. The number of bits in the network portion of the address are converted to 1s and right padded with 0s until there are 32 numbers. The sequence of numbers is then divided into 4 octets.

## What is the CIDR value for the subnet mask?

255.255.255.192 /26 64
255.255.255.128 /25 128
255.255.255.0 /24 256
255.255.254.0 /23 512

How do you calculate subnet mask?

IPv4 addresses are 32 bits made up of four octets of 8 bits each. To calculate the subnet mask, convert an IP address to binary, perform the calculation and then convert back to the IPv4 decimal number representation known as a dotted quad. The same subnetting procedure works for IPv6 addresses.

A more mathematical way to express the the subnet mask calculation is: current value = value on the left (previous value) + power of 2 of this column. It should take about 1 minute to do this when the exam starts. It will be extremely useful all through the exam to double check any IP and subnet.

How to determine a custom subnet mask?

Determining The Custom Subnet Mask Using Subnetting Tables. Now, what could be easier than that? Well, you could simply refer to the subnetting summary tables. Find the table for the appropriate class, and then find the row that you selected in the previous step that matches the number of subnet ID bits you want to use. You can see the matching subnet mask right there. (Hey, it’s good to know how to do it yourself! You may not always have tables to refer to!)

### How to calculate IP and subnet mask?

How to Calculate Subnet Mask from IP Address Step by Step Find Subnet Number Subtract Prefix Number from /32 32-29=3 Calculate Subnet Mask 8 Bits – 3 Bits = 5 Bits (Network Bits Turned On) You might be asking Find Subnet Size Raise 2 to the power of deduction (8-3 =5 Bits). Let’s call the bits n! Find Broadcast Address Subnet Size – 1 (2**n) – 1 = Broadcast Address (2**3) – 1 = (8-1) = 7