/9 Subnet: Mask 255.128.0.0, 8,388,606 Usable Hosts
A /9 subnet has a subnet mask of 255.128.0.0 and contains 8,388,608 total IP addresses, of which 8,388,606 are usable host addresses (the network and broadcast addresses are reserved). A /9 contains 32,768 /24 networks.
| CIDR notation | /9 |
|---|---|
| Subnet mask | 255.128.0.0 |
| Wildcard mask | 0.127.255.255 |
| Mask in binary | 11111111.10000000.00000000.00000000 |
| Total addresses | 8,388,608 (2^23) |
| Usable hosts | 8,388,606 |
| Host bits | 23 |
Usable hosts in a /9 by platform
Cloud providers reserve more than the usual two addresses per subnet, so the same /9 gives you fewer usable IPs in the cloud than on a standard LAN.
| Platform | Reserved IPs | Usable hosts |
|---|---|---|
| Standard (network + broadcast) | 2 | 8,388,606 |
| AWS VPC | 5 | 8,388,603 |
| Microsoft Azure VNet | 5 | 8,388,603 |
| Google Cloud VPC | 4 | 8,388,604 |
| Oracle Cloud VCN | 3 | 8,388,605 |
Good to know
A /9 subnet has a 255.128.0.0 mask and 8,388,608 total addresses (8,388,606 usable). Each step from /9 to /10 halves the block; each step back to /8 doubles it.
How a /9 is calculated
- The /9 means the first 9 bits are the network portion, leaving 23 host bits.
- Total addresses = 2^(32 - 9) = 2^23 = 8,388,608.
- Usable hosts (standard) = 8,388,608 - 2 (network + broadcast) = 8,388,606.
- Subnet mask = 255.128.0.0; wildcard mask = 0.127.255.255.
Want to split a /9 into smaller subnets, see every address range, or plan a VLSM layout? Open the free subnet calculator →