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Subnetting

Introduction

Subnetting can be ponderous. This post acts as a repository for subnetting information that is important for the job. It has a link to one of my favorite subnetting calculators, and it contains subnetting tables for IPv4 class A, B, and C networks. A lot of the work that a tech will do includes classless also. See this page for a description of classful versus classless IP. Watch the following video covering an introduction to subnetting.

Video

Online Subnetting Calculator

Subnetting Tables

Class A Subnetting

Subnet ID Mask # masked bits # of subnets # of usable hosts per subnet
0 255.0.0.0 /8 N/A 16,777,214
1 255.128.0.0 /9 2 8,388,606
2 255.192.0.0 /10 4 4,194,302
3 255.224.0.0 /11 8 2,097,150
4 255.240.0.0 /12 16 1,048,574
5 255.248.0.0 /13 32 524,286
6 255.252.0.0 /14 64 262,142
7 255.254.0.0 /15 128 131,070
8 255.255.0.0 /16 256 65,534
9 255.255.128.0 /17 512 32,766
10 255.255.192.0 /18 1,024 16,382
11 255.255.224.0 /19 2,048 8,190
12 255.255.240.0 /20 4,096 4,094
13 255.255.248.0 /21 8,192 2,046
14 255.255.252.0 /22 16,384 1,022
15 255.255.254.0 /23 32,768 510
16 255.255.255.0 /24 65,536 254
17 255.255.255.128 /25 131,072 126
18 255.255.255.192 /26 262,144 62
19 255.255.255.224 /27 524,288 30
20 255.255.255.240 /28 1,048,576 14
21 255.255.255.248 /29 2,097,152 6
22 255.255.255.252 /30 4,194,304 2
23 255.255.255.254 /31 N/A N/A
24 255.255.255.255 /32 N/A N/A

Class B Subnetting

Subnet ID Mask # masked bits # of subnets # of usable hosts per subnet
0 255.255.0.0 /16 N/A 65,534
1 255.255.128.0 /17 2 32,766
2 255.255.192.0 /18 4 16,382
3 255.255.224.0 /19 8 8,190
4 255.255.240.0 /20 16 4,094
5 255.255.248.0 /21 32 2,046
6 255.255.252.0 /22 64 1,022
7 255.255.254.0 /23 128 510
8 255.255.255.0 /24 256 254
9 255.255.255.128 /25 512 126
10 255.255.255.192 /26 1,024 62
11 255.255.255.224 /27 2,048 30
12 255.255.255.240 /28 4,096 14
13 255.255.255.248 /29 8,192 6
14 255.255.255.252 /30 16,384 2
15 255.255.255.254 /31 N/A N/A
16 255.255.255.255 /32 N/A N/A

Class C Subnetting

Subnet ID Mask # masked bits # of subnets # of usable hosts per subnet
0 255.255.255.0 /24 N/A 254
1 255.255.255.128 /25 2 126
2 255.255.255.192 /26 4 62
3 255.255.255.224 /27 8 30
4 255.255.255.240 /28 16 14
5 255.255.255.248 /29 32 6
6 255.255.255.252 /30 64 2
7 255.255.255.254 /31 N/A N/A
8 255.255.255.255 /32 N/A N/A