A /28 subnet mask is a subnet mask that divides a larger network into multiple smaller subnetworks. Each of the subnetworks will have a maximum of 16 IP address ranges. The first IP address in this range is used as the network address, while the last IP address in this range is reserved as the broadcast address. Hence, there are 14 usable IP addresses in a /28 subnet mask.
For instance, if we subnet the network 192.168.2.0/24 with a /28 subnet mask, the first subnet will have the network address 192.168.2.0, a usable IP range from 192.168.2.1 to 192.168.2.14, and the broadcast address of 192.168.2.15. The second subnet will have a network address of 192.168.2.16, a usable IP range of 192.168.2.17 to 192.168.2.30, a broadcast address of 192.168.2.31, and so on.
Here is a table of a network subnetted with a /28 subnet mask:
| Network Address | Usable IP addresses | Broadcast IP address |
|---|---|---|
| .0 | .1-.14 | .15 |
| .16 | .17-.30 | .31 |
| .32 | .33-.46 | .47 |
| .48 | .49-.62 | .63 |
| .64 | .65-.78 | .79 |
| .80 | .81-.94 | .95 |
| .96 | .77-.110 | .111 |
| .112 | .113-.126 | .127 |
| .128 | .129-.142 | .143 |
| .144 | .145-.158 | .159 |
| .160 | .161-.174 | .175 |
| .176 | .177-.190 | .191 |
| .192 | .193-.206 | .207 |
| .208 | .209-.222 | .223 |
| .224 | .225-.238 | .239 |
| .240 | .241-.254 | .255 |
/28 Subnet Mask Usable IP Address
In /28 subnet mask, there are 16 ranges of IP addresses; the first one in the range is the network address, and the last IP address in this range is the broadcast IP address. Hence, there are 14 usable IP addresses in the /28 subnet mask.
/28 Subnet Mask Dotted Decimal Notation
The dotted decimal notation for a /28 subnet mask is 255.255.255.240. This representation is gotten by setting the first 28 bits of the 32-bit IPv4 address to ‘1s’, setting the remaining 4 bits to ‘0s’, and converting from binary to decimals.
/28 Wildcard Mask
The wildcard mask for /28 prefix length is 0.0.0.15. This is gotten by subtracting each octet of the subnet mask from 255.
Subnetting Class C Network with /28 Subnet Mask
To subnet a Class C network with a /28 subnet mask, 4 bits are borrowed from the host bit to the network bits, leaving 4 host bits.
So, the number of subnetwork obtainable when we subnet a class C network with /28 prefix length is gotten as follow;
2^4 = 16
Therefore, subnetting a Class C network with a /28 prefix length divides the network into 16 subnetworks, each having 16 IP address ranges.
Subnetting Class B Network with /28 Subnet Mask
To subnet a Class B network with a /28 prefix length, 12 bits are borrowed from the host bits and added to the network bits.
Hence, the number of subnetworks obtainable when a class B network is subnetted with a /28 prefix length is obtained as follows:
2^12 = 4096.
Therefore, a /28 subnet mask will divide a class B network into 4096 subnetworks, with each subnetwork having 16 ranges of IP addresses.
Subnetting Class A Network with /28 Subnet Mask
To subnet a class A network with a /28 prefix length, 20 bits need to be borrowed from the host bits and added to the network bits.
So, the number of subnetworks obtainable when we subnet a class A network with a /28 prefix length is as follows:
2^20 = 1048576
Therefore, a /28 subnet mask will divide a class A network into 1048576 subnetworks. Each subnetwork will have 16 ranges of IP addresses.
How Many host in /28
There are a total of 16 ranges of IP addresses in a /28 subnet mask. The first IP address in this range is the network address, and the last IP address in this range is the broadcast IP address. Therefore, there are 14 free IP addresses that can be assigned to a host in a /28 subnet mask.
How Many Subnets in /28
The number of subnetworks obtainable when we subnet with a /28 subnet mask depends on the class of the network. The class C network will yield 16 subnetworks, the class B network will yield 4096 subnetworks, and the class A network will yield 1048576 subnetworks when subnetted with the /28 prefix length.
Conclusion
The /28 subnet mask generally provides 16 IP address ranges per subnetwork. The first IP address in this range is reserved as the network address, and the last IP address in this range is reserved as the broadcast IP addresses. So, there are 14 usable IP addresses available to host devices.
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