Subnet Mask
/23 Subnet Mask
A /23 prefix means the subnet mask is 255.255.254.0. It has 9 host bits, giving 512 total addresses and 510 usable hosts.
/23 at a glance
| Property | Value |
|---|---|
| CIDR prefix | /23 |
| Subnet mask | 255.255.254.0 |
| Wildcard mask | 0.0.1.255 |
| Total addresses | 512 |
| Usable hosts | 510 |
| Host bits | 9 |
How it is calculated
A /23 sets the first 23 bits to 1 (network) and the remaining 9 bits to 0 (host). Usable hosts = 29 − 2 = 510.
The wildcard mask 0.0.1.255 is the inverse — used in Cisco ACLs and OSPF network statements.
Frequently asked questions
What is a /23 subnet mask?
A /23 equals 255.255.254.0 in dotted decimal (wildcard 0.0.1.255). It provides 512 total addresses and 510 usable hosts.
How many hosts are in a /23?
A /23 has 9 host bits, so it supports 510 usable hosts.
What is the wildcard mask for /23?
The wildcard (inverse) mask for /23 is 0.0.1.255, used in Cisco ACLs and OSPF statements.
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