What is a /25 subnet?
126 usable hosts out of 128 addresses, behind netmask 255.255.255.128.
| Prefix | /25 |
|---|---|
| Netmask | 255.255.255.128 |
| Wildcard | 0.0.0.127 |
| Total addresses | 128 |
| Usable hosts | 126 |
| Example block | 10.0.0.0/25 |
| Usable host range | 10.0.0.1 – 10.0.0.126 |
| Broadcast | 10.0.0.127 |
A /25 fixes the first 25 bits of the address as the network and leaves 7 for hosts — 128 addresses in all.
Of those, 126 can be given to a machine: the first address names the network itself, and the last is the broadcast address.
These are the everyday sizes. A /24 is one office, one VLAN or one cloud subnet; the smaller ones suit a rack, a service tier or a DMZ.
2 of them fit inside a /24.
Other subnet sizes
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