/25 subnet (255.255.255.128)
A /25 network has 128 addresses, of which 126 can be given to hosts after the network and broadcast addresses. Part of a /24, used to split one class C-sized network into smaller segments.
- CIDR notation
- /25
- Subnet mask
- 255.255.255.128
- Wildcard mask
- 0.0.0.127
- Binary mask
- 11111111.11111111.11111111.10000000
- Total addresses
- 128
- Usable hosts
- 126
- Example network
- 192.168.1.0/25
- Example usable range
- 192.168.1.1 – 192.168.1.126
- /25 networks in a /24
- 2
Calculate a /25 for your own address
192.168.1.0/24 split into /25 networks
| Network | Usable range | Broadcast |
|---|---|---|
| 192.168.1.0/25 | 192.168.1.1 – 192.168.1.126 | 192.168.1.127 |
| 192.168.1.128/25 | 192.168.1.129 – 192.168.1.254 | 192.168.1.255 |
In firewall rules and investigations
A /25 rule matches every address from 192.168.1.0 to 192.168.1.127. In Cisco ACLs the same range is written with the wildcard mask 0.0.0.127. When an alert names an IP, checking whether it falls inside a known /25 (your own network, a cloud provider’s published range or a blocked range) is often the quickest first step.