Network - (Network|Subnet) Mask

> NetWork

1 - About

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

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3 - Notation

Mask can be defined via:

3.1 - dot-decimal

dot-decimal notation.

Example:

255.255.255.000

3.2 - Prefix

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

Example

1111111 0000000 0000000 0000000  = 8 leading 1 bits = prefix of /8

Larger values indicate smaller networks.

The prefix length is used in the CIDR notation.

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3.3 - Binary

Example:

1111111 0000000 0000000 000000

4 - Table

Prefix size Network mask Usable hosts per subnet
/1 128.0.0.0 2,147,483,646
/2 192.0.0.0 1,073,741,822
/3 224.0.0.0 536,870,910
/4 240.0.0.0 268,435,454
/5 248.0.0.0 134,217,726
/6 252.0.0.0 67,108,862
/7 254.0.0.0 33,554,430
Class A
/8 255.0.0.0 16,777,214
/9 255.128.0.0 8,388,606
/10 255.192.0.0 4,194,302
/11 255.224.0.0 2,097,150
/12 255.240.0.0 1,048,574
/13 255.248.0.0 524,286
/14 255.252.0.0 262,142
/15 255.254.0.0 131,070
Class B
/16 255.255.0.0 65,534
/17 255.255.128.0 32,766
/18 255.255.192.0 16,382
/19 255.255.224.0 8,190
/20 255.255.240.0 4,094
/21 255.255.248.0 2,046
/22 255.255.252.0 1,022
/23 255.255.254.0 510
Class C
/24 255.255.255.0 254
/25 255.255.255.128 126
/26 255.255.255.192 62
/27 255.255.255.224 30
/28 255.255.255.240 14
/29 255.255.255.248 6
/30 255.255.255.252 2
/31 255.255.255.254 0
/32 255.255.255.255 0
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5 - Documentation / Reference

network/mask.txt · Last modified: 2019/05/03 21:36 by gerardnico