How to fill in the subnet mask

The subnet mask divides the IP address into a network address and a host address. The steps to fill in are as follows: Determine the subnet size and convert it into a bit mask. Converts a binary bitmask to dotted decimal. Example: Create a subnet (/27) with 30 hosts, using subnet mask 255.255.255.192.

How to fill in the subnet mask?

A subnet mask is a 32-bit binary number used to divide an IP address into a network address and a host address. The following steps explain how to fill in the subnet mask:

1. Determine the network size

Determine the size of the subnet to be created. Typically the following subnet sizes are used:

• /24: 255 hosts
• /27: 30 hosts
• /30: 2 hosts

2. Convert the subnet size to a bitmask

Convert the subnet size to a bitmask as follows:

• Subtract the subnet size from 32 (for example, /24 = 32 - 24 = 8)
• Convert the result to a binary number (for example, 8 = 1000)
• Add 1 in front of the binary number (For example, 1000 = 1111111111111111111111100000000)

3. Convert binary mask to dotted decimal

Convert binary mask to dotted decimal, method As follows:

• Split the binary mask into 8-bit blocks
• Convert each 8-bit block to a decimal number (0-255)
• Split these four Decimal numbers separated by dots (for example, 11111111.11111111.11111111.00000000 = 255.255.255.0)

Example:

To create a subnet with 30 hosts (/ 27), please do the following:

• 32 - 27 = 5
• 5 The binary number is 101
• Add 1 to get the binary mask: 11111111.11111111. 11111111.11000000
• Dotted decimal mask: 255.255.255.192

Therefore, the /27 subnet mask is 255.255.255.192.

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