/17 Subnet: Mask 255.255.128.0, 32,766 Usable Hosts
A /17 subnet has a subnet mask of 255.255.128.0 and contains 32,768 total IP addresses, of which 32,766 are usable host addresses (the network and broadcast addresses are reserved). A /17 contains 128 /24 networks.
| CIDR notation | /17 |
|---|---|
| Subnet mask | 255.255.128.0 |
| Wildcard mask | 0.0.127.255 |
| Mask in binary | 11111111.11111111.10000000.00000000 |
| Total addresses | 32,768 (2^15) |
| Usable hosts | 32,766 |
| Host bits | 15 |
Usable hosts in a /17 by platform
Cloud providers reserve more than the usual two addresses per subnet, so the same /17 gives you fewer usable IPs in the cloud than on a standard LAN.
| Platform | Reserved IPs | Usable hosts |
|---|---|---|
| Standard (network + broadcast) | 2 | 32,766 |
| AWS VPC | 5 | 32,763 |
| Microsoft Azure VNet | 5 | 32,763 |
| Google Cloud VPC | 4 | 32,764 |
| Oracle Cloud VCN | 3 | 32,765 |
Good to know
A /17 subnet has a 255.255.128.0 mask and 32,768 total addresses (32,766 usable). Each step from /17 to /18 halves the block; each step back to /16 doubles it.
How a /17 is calculated
- The /17 means the first 17 bits are the network portion, leaving 15 host bits.
- Total addresses = 2^(32 - 17) = 2^15 = 32,768.
- Usable hosts (standard) = 32,768 - 2 (network + broadcast) = 32,766.
- Subnet mask = 255.255.128.0; wildcard mask = 0.0.127.255.
Want to split a /17 into smaller subnets, see every address range, or plan a VLSM layout? Open the free subnet calculator →