/23 Subnet
512 IPs — two /24s combined
A /23 covers two consecutive /24 subnets (512 total addresses, 510 usable). Handy when you need slightly more than a /24 provides without jumping all the way to a /22.
Common Use Cases
- → Two-floor office network
- → Expanded department VLAN
- → Route aggregation of two /24s
Example /23 Networks
| CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|
| 10.0.0.0/23 | 10.0.0.0 | 10.0.0.1 | 10.0.1.254 | 10.0.1.255 | 510 |
| 172.16.0.0/23 | 172.16.0.0 | 172.16.0.1 | 172.16.1.254 | 172.16.1.255 | 510 |
| 172.31.0.0/23 | 172.31.0.0 | 172.31.0.1 | 172.31.1.254 | 172.31.1.255 | 510 |
| 192.168.0.0/23 | 192.168.0.0 | 192.168.0.1 | 192.168.1.254 | 192.168.1.255 | 510 |
| 192.168.0.0/23 | 192.168.0.0 | 192.168.0.1 | 192.168.1.254 | 192.168.1.255 | 510 |
| 10.0.0.0/23 | 10.0.0.0 | 10.0.0.1 | 10.0.1.254 | 10.0.1.255 | 510 |
How /23 Compares
| Prefix | Total IPs | Usable Hosts | Subnet Mask | Typical Use |
|---|---|---|---|---|
| /20 | 4,096 | 4,094 | 255.255.240.0 | AWS default subnet, medium office VLAN |
| /21 | 2,048 | 2,046 | 255.255.248.0 | Enterprise building / large app tier |
| /22 | 1,024 | 1,022 | 255.255.252.0 | Medium office/application segment |
| /23 ◀ | 512 | 510 | 255.255.254.0 | Aggregated /24 pair |
| /24 | 256 | 254 | 255.255.255.0 | Standard subnet — home, office, cloud |
| /25 | 128 | 126 | 255.255.255.128 | Half a /24 — public/private split |
| /26 | 64 | 62 | 255.255.255.192 | Cloud per-tier subnet, small VLAN |
Frequently Asked Questions
How many IPs are in a /23?
A /23 subnet contains 512 total IP addresses and 510 usable host addresses. The network address (first IP) and broadcast address (last IP) are reserved and cannot be assigned to hosts.
What is the subnet mask for /23?
The subnet mask for a /23 is 255.255.254.0.
In CIDR notation, the prefix length /23 means
the first 23 bits of the address are the network portion.
The wildcard (inverse) mask is 0.0.1.255.
How many /23 subnets fit in a /22?
Exactly 2 — a /22 can be split into two /23 subnets of equal size. Each /23 subnet has 510 usable hosts, compared to 1,022 in the parent /22.