A /25 splits a /24 in half: 128 addresses, 126 usable, mask 255.255.255.128. The two halves are .0–.127 and .128–.255. It’s handy for separating, say, office devices from guest devices without renumbering the whole network. Subnetting questions love it because the block size of 128 makes the halves easy to see.
Facts
- Prefix
- /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 range
- 192.168.1.0/25: 192.168.1.0 – 192.168.1.127
- Typical use
- Half of a /24, for splitting a small network in two.
Try it
Try: , ,
- CIDR block
- 192.168.1.0/25
- IP range
- 192.168.1.0 – 192.168.1.127
- Addresses
- 128
- Usable hosts
- 126
- Subnet mask
- 255.255.255.128
- Wildcard mask
- 0.0.0.127
Frequently asked questions
How many hosts are in a /25?
A /25 has 128 addresses. Subtracting the network and broadcast addresses leaves 126 usable hosts.
What is the subnet mask for /25?
/25 is 255.255.255.128 (wildcard mask 0.0.0.127). In binary that’s 25 ones followed by 7 zeros.