How Many IPs in a /25?
128 addresses, 126 usable, mask 255.255.255.128.
A /25 is half of a /24, often used to split one /24 into two segments such as servers and clients.
| Subnet mask | 255.255.255.128 |
|---|---|
| Wildcard mask | 0.0.0.127 |
| Total addresses | 128 |
| Usable hosts | 126 |
| In /24 terms | 2 of them fit in one /24. |
| Example (10.0.0.0/25) | 10.0.0.0 - 10.0.0.127 |
Usable addresses in cloud subnets
Cloud providers reserve extra addresses in every subnet, so fewer than 126 are available to your machines.
| AWS | 123 usable |
|---|---|
| Azure | 123 usable |
| Google Cloud | 124 usable |
| Oracle Cloud | 125 usable |
Limits and reserved counts are commonly documented values; check your provider's current documentation before you plan around them.
Other sizes
/22 | /23 | /25 | /26 | /27 | /28
Split a block into /25 subnets with the subnet splitter, or calculate any block with the CIDR calculator.
FAQ
How many usable IP addresses are in a /25?
126 usable addresses out of 128. The network and broadcast addresses are reserved.
What is the subnet mask for /25?
255.255.255.128, with wildcard mask 0.0.0.127.
How many usable addresses does a /25 have in AWS?
123, because AWS reserves five addresses in every subnet.