The /9 subnet
A /9 subnet uses the mask 255.128.0.0 and holds 8,388,608 addresses, 8,388,606 of them usable.
A /9 is a large network of 8,388,608 addresses, 8,388,606 of them usable, with the mask 255.128.0.0. It is bigger than most single sites need and is usually subdivided.
Address plans use a /9 as a site-level or campus-level supernet, then split it into /24s or smaller per VLAN. The wildcard 0.127.255.255 matches the whole block in an access list.
Below you can see the exact network, broadcast, and host range for any /9 you enter, calculated instantly in your browser.
Calculate a /9 network
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
10101100.00010000.00000000.0000000011111111.10000000.00000000.00000000Example: 172.16.0.0/9
Taking 172.16.0.0/9 as a worked example, the block breaks down like this:
| Network address | 172.0.0.0 |
|---|---|
| Usable range | 172.0.0.1 - 172.127.255.254 |
| Broadcast address | 172.127.255.255 |
| Total addresses | 8,388,608 |
| Usable hosts | 8,388,606 |
| Size | 128 class B blocks |
Frequently asked questions
What is the subnet mask for a /9?
A /9 uses the subnet mask 255.128.0.0. Its wildcard mask, used in access lists, is 0.127.255.255.
How many hosts are in a /9 subnet?
A /9 has 8,388,608 total addresses and 8,388,606 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /9 used for?
Large network. It is equivalent to 128 class B blocks.
How do I calculate a /9 network?
Set the host bits to zero for the network address and to one for the broadcast address. The calculator on this page does it for any /9 block you enter.