The /23 subnet
A /23 subnet uses the mask 255.255.254.0 and holds 512 addresses, 510 of them usable.
A /23 sits between a /16 and a /24: 512 addresses, 510 usable, mask 255.255.254.0. It is a common size for a large flat segment or for aggregating several /24s into one route.
Summarizing contiguous /24s into a /23 keeps routing tables small. The block still fits inside a single broadcast domain if you want it to, though most designs subnet it further.
Below you can see the exact network, broadcast, and host range for any /23 you enter, calculated instantly in your browser.
Calculate a /23 network
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
11000000.00000000.00000010.0000000011111111.11111111.11111110.00000000Example: 192.0.2.0/23
Taking 192.0.2.0/23 as a worked example, the block breaks down like this:
| Network address | 192.0.2.0 |
|---|---|
| Usable range | 192.0.2.1 - 192.0.3.254 |
| Broadcast address | 192.0.3.255 |
| Total addresses | 512 |
| Usable hosts | 510 |
| Size | 2 class C blocks |
Frequently asked questions
What is the subnet mask for a /23?
A /23 uses the subnet mask 255.255.254.0. Its wildcard mask, used in access lists, is 0.0.1.255.
How many hosts are in a /23 subnet?
A /23 has 512 total addresses and 510 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /23 used for?
Standard LAN size. It is equivalent to 2 class C blocks.
How do I calculate a /23 network?
Set the host bits to zero for the network address and to one for the broadcast address. The calculator on this page does it for any /23 block you enter.