A /17 subnet mask is 255.255.128.0, with 32,768 addresses and 32,766 usable hosts.
| CIDR prefix | /17 |
|---|---|
| Subnet mask | 255.255.128.0 |
| Subnet mask (binary) | 11111111.11111111.10000000.00000000 |
| Wildcard mask | 0.0.127.255 |
| Network bits / host bits | 17 / 15 |
| Total addresses | 32,768 |
| Usable hosts | 32,766 |
| /17 subnets in a /8 | 512 |
| /17 subnets in a /16 | 2 |
The mask ends 1 bit into octet 3, so blocks step in increments of 128 in that octet.
| Network | First usable host | Last usable host | Broadcast |
|---|---|---|---|
| 192.168.0.0/17 | 192.168.0.1 | 192.168.127.254 | 192.168.127.255 |
| 192.168.128.0/17 | 192.168.128.1 | 192.168.255.254 | 192.168.255.255 |
A /17 subnet mask is 255.255.128.0. In binary that is 11111111.11111111.10000000.00000000: 17 network bits followed by 15 host bits. The wildcard mask is 0.0.127.255.
A /17 holds 32,768 addresses in total. Subtracting the network and broadcast addresses leaves 32,766 usable hosts.
A /16 divides into 2 subnets of size /17, because each extra mask bit doubles the number of subnets.
Calculate this over HTTP: curl https://networkcalc.com/api/ip/192.168.1.0/17.
See the Subnet Calculator API.