/23 Subnet: Mask 255.255.254.0, 510 Usable Hosts

A /23 subnet has a subnet mask of 255.255.254.0 and contains 512 total IP addresses, of which 510 are usable host addresses (the network and broadcast addresses are reserved). A /23 contains 2 /24 networks.

Usable hosts in a /23 by platform

Cloud providers reserve more than the usual two addresses per subnet, so the same /23 gives you fewer usable IPs in the cloud than on a standard LAN.

Good to know

A /23 (512 addresses) doubles a /24. It is handy when 254 hosts is just slightly too few but you do not want to jump to a /22.

How a /23 is calculated

• The /23 means the first 23 bits are the network portion, leaving 9 host bits.
• Total addresses = 2^(32 - 23) = 2^9 = 512.
• Usable hosts (standard) = 512 - 2 (network + broadcast) = 510.
• Subnet mask = 255.255.254.0; wildcard mask = 0.0.1.255.