A /9 is half of a /8: the first octet plus one more bit is fixed, so the second octet runs 0–127 or 128–255. Blocks this size are rare in practice. They show up when an organisation that holds a /8 splits it in two, or in routing tables that summarise large ISP allocations. Inside a private network you would almost never configure a single subnet this big.
Facts
- Prefix
- /9
- Subnet mask
- 255.128.0.0
- Wildcard mask
- 0.127.255.255
- Binary mask
- 11111111.10000000.00000000.00000000
- Total addresses
- 8,388,608
- Usable hosts
- 8,388,606
- Example range
- 10.0.0.0/9: 10.0.0.0 – 10.127.255.255
- Typical use
- Very large allocations to ISPs and big organisations.
Try it
Try: , ,
- CIDR block
- 10.0.0.0/9
- IP range
- 10.0.0.0 – 10.127.255.255
- Addresses
- 8,388,608
- Usable hosts
- 8,388,606
- Subnet mask
- 255.128.0.0
- Wildcard mask
- 0.127.255.255
Frequently asked questions
How many hosts are in a /9?
A /9 has 8,388,608 addresses. Subtracting the network and broadcast addresses leaves 8,388,606 usable hosts.
What is the subnet mask for /9?
/9 is 255.128.0.0 (wildcard mask 0.127.255.255). In binary that’s 9 ones followed by 23 zeros.