What is a /17 subnet?
32,766 usable hosts out of 32,768 addresses, behind netmask 255.255.128.0.
| Prefix | /17 |
|---|---|
| Netmask | 255.255.128.0 |
| Wildcard | 0.0.127.255 |
| Total addresses | 32,768 |
| Usable hosts | 32,766 |
| Example block | 10.0.0.0/17 |
| Usable host range | 10.0.0.1 – 10.0.127.254 |
| Broadcast | 10.0.127.255 |
A /17 fixes the first 17 bits of the address as the network and leaves 15 for hosts — 32,768 addresses in all.
Of those, 32,766 can be given to a machine: the first address names the network itself, and the last is the broadcast address.
This is the usual size for a VPC or a site: room for tens of thousands of addresses, divided into smaller subnets per zone or per service.
It is 128 times the size of a /24.
Other subnet sizes
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