/28 Subnet Mask

A /28 subnet mask is 255.255.255.240. It has 16 addresses, 14 usable hosts and the wildcard mask 0.0.0.15.

CIDR prefix/28
Subnet mask255.255.255.240
Wildcard mask0.0.0.15
Binary mask11111111.11111111.11111111.11110000
Total addresses16
Usable hosts14
Block size16 (fourth octet)

Example: 192.168.1.0/28

Network address192.168.1.0
First usable host192.168.1.1
Last usable host192.168.1.14
Broadcast address192.168.1.15

Where /28 subnets start

/28 networks start on multiples of 16 in the fourth octet (0, 16, 32, 48, …). A /24 holds 16 /28 subnets, and a /16 holds 4,096.

How to calculate a /28 subnet

  1. Host bits: 32 − 28 = 4.
  2. Total addresses: 24 = 16.
  3. Usable hosts: 16 − 2 = 14, because the network and broadcast addresses can't be assigned to hosts.
  4. Subnet mask: 28 one-bits followed by 4 zero-bits. The fourth octet is 240 (256 − 16), which gives 255.255.255.240.
  5. Wildcard mask: 255.255.255.255 − 255.255.255.240 = 0.0.0.15.

When to use a /28

A /28 splits a /24 into sixteen subnets of 14 usable hosts each. It suits small segments such as management networks or a DMZ.

Updated . Calculate any network with the subnet calculator, or compare all prefixes in the subnet cheat sheet.