What is a /9 subnet?
8,388,606 usable hosts out of 8,388,608 addresses, behind netmask 255.128.0.0.
| Prefix | /9 |
|---|---|
| Netmask | 255.128.0.0 |
| Wildcard | 0.127.255.255 |
| Total addresses | 8,388,608 |
| Usable hosts | 8,388,606 |
| Example block | 10.0.0.0/9 |
| Usable host range | 10.0.0.1 – 10.127.255.254 |
| Broadcast | 10.127.255.255 |
A /9 fixes the first 9 bits of the address as the network and leaves 23 for hosts — 8,388,608 addresses in all.
Of those, 8,388,606 can be given to a machine: the first address names the network itself, and the last is the broadcast address.
A block this large is an allocation rather than a subnet — a whole private range to carve up, or something a regional registry hands out. You would not put hosts directly in it.
It is 32,768 times the size of a /24.
Other subnet sizes
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