Network - (Network|Subnet) Mask

Card Puncher Data Processing


subnet mask is the second part of an Ip address. It's also called the mask of a subnet because all hosts on a subnet have the same network mask.

The maximum size of the network is given by the number of addresses that are possible with the remaining, least-significant bits in the mask below the prefix. See table


Mask can be defined via:


The dot-decimal notation separated the byte with a dot converted in decimal.

Example in ipv4


The (routing) prefix is the number of leading 1 bits.

Example with an ipv4 address

11111111 00000000 00000000 00000000  = 8 leading 1 bits = prefix of /8

Larger values indicate smaller networks. See the table below.

The prefix length is used in the CIDR notation.



1111111 0000000 0000000 000000


Mask Format

Prefix size Network mask Usable hosts per subnet
/1 2,147,483,646
/2 1,073,741,822
/3 536,870,910
/4 268,435,454
/5 134,217,726
/6 67,108,862
/7 33,554,430
Class A
/8 16,777,214
/9 8,388,606
/10 4,194,302
/11 2,097,150
/12 1,048,574
/13 524,286
/14 262,142
/15 131,070
Class B
/16 65,534
/17 32,766
/18 16,382
/19 8,190
/20 4,094
/21 2,046
/22 1,022
/23 510
Class C
/24 254
/25 126
/26 62
/27 30
/28 14
/29 6
/30 2
/31 0
/32 0

Documentation / Reference

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