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
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