/25 Subnet
126 usable hosts — half a /24
A /25 divides a standard /24 in half, yielding two subnets of 128 addresses each (126 usable). Commonly used to split a /24 into a public-facing half and a private/internal half.
Common Use Cases
- → Public vs private half of a /24
- → Department sub-segment
- → Smaller cloud application subnets
Example /25 Networks
| CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|
| 10.0.0.0/25 | 10.0.0.0 | 10.0.0.1 | 10.0.0.126 | 10.0.0.127 | 126 |
| 172.16.0.0/25 | 172.16.0.0 | 172.16.0.1 | 172.16.0.126 | 172.16.0.127 | 126 |
| 172.31.0.0/25 | 172.31.0.0 | 172.31.0.1 | 172.31.0.126 | 172.31.0.127 | 126 |
| 192.168.0.0/25 | 192.168.0.0 | 192.168.0.1 | 192.168.0.126 | 192.168.0.127 | 126 |
| 192.168.1.0/25 | 192.168.1.0 | 192.168.1.1 | 192.168.1.126 | 192.168.1.127 | 126 |
| 10.0.1.0/25 | 10.0.1.0 | 10.0.1.1 | 10.0.1.126 | 10.0.1.127 | 126 |
How /25 Compares
| Prefix | Total IPs | Usable Hosts | Subnet Mask | Typical Use |
|---|---|---|---|---|
| /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 |
| /27 | 32 | 30 | 255.255.255.224 | Small workgroup / management subnet |
| /28 | 16 | 14 | 255.255.255.240 | AWS NAT/endpoint dedicated subnet |
Frequently Asked Questions
How many IPs are in a /25?
A /25 subnet contains 128 total IP addresses and 126 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 /25?
The subnet mask for a /25 is 255.255.255.128.
In CIDR notation, the prefix length /25 means
the first 25 bits of the address are the network portion.
The wildcard (inverse) mask is 0.0.0.127.
How many /25 subnets fit in a /24?
Exactly 2 — a /24 can be split into two /25 subnets of equal size. Each /25 subnet has 126 usable hosts, compared to 254 in the parent /24.