/27 Subnet Mask

A /27 subnet mask is 255.255.255.224. It has 32 addresses, 30 usable hosts and the wildcard mask 0.0.0.31.

CIDR prefix/27
Subnet mask255.255.255.224
Wildcard mask0.0.0.31
Binary mask11111111.11111111.11111111.11100000
Total addresses32
Usable hosts30
Block size32 (fourth octet)

Example: 192.168.1.0/27

Network address192.168.1.0
First usable host192.168.1.1
Last usable host192.168.1.30
Broadcast address192.168.1.31

Where /27 subnets start

/27 networks start on multiples of 32 in the fourth octet (0, 32, 64, 96, …). A /24 holds 8 /27 subnets, and a /16 holds 2,048.

How to calculate a /27 subnet

  1. Host bits: 32 − 27 = 5.
  2. Total addresses: 25 = 32.
  3. Usable hosts: 32 − 2 = 30, because the network and broadcast addresses can't be assigned to hosts.
  4. Subnet mask: 27 one-bits followed by 5 zero-bits. The fourth octet is 224 (256 − 32), which gives 255.255.255.224.
  5. Wildcard mask: 255.255.255.255 − 255.255.255.224 = 0.0.0.31.

When to use a /27

A /27 splits a /24 into eight subnets of 30 usable hosts each.

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