Subnetting Tables and Tools

Subnetting can be ponderous. This post acts as a repository for subnetting information that is pertinent to certification exams and is important for the job. It contains subnetting tables for IPv4 class A, B, and C networks. It also has various links including two of my favorite subnetting calculators.

Watch my introductory lesson on subnetting here:

Tools

Online IP Subnet Calculator: An excellent utility which can quickly tell you how many subnets and how many hosts per subnet can be used in any given subnetted class A, B, or C network.

PHP Subnet Calculator: Another great utility that shows each subnet ID starting range (does IPv6 also). Not as user-friendly, but still very functional. To make it work, enter something such as 192.168.1.0/24 (no spaces) in the “Network & CIDR” field, and then the subnet mask you wish to use to subdivide that network, for example /28 in the “subnet CIDR” field. That should display all the subnet ID starting points for that subnet mask.

Network IP/Subnet Calculator: Nice little free tool for your Android device. As always, read up on Android apps before installing them so you will be sure it is compatible… and won’t cause any conflicts or other problems with your mobile device.

Learn More

And consider books: IP Subnetting Made Easy and Mastering Binary Math and Subnetting are two inexpensive Kindle downloads that can help to reinforce your understanding of subnetting.

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

 

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