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 |
