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/9 Subnet Mask

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A /9 subnet mask is 255.128.0.0, with 8,388,608 addresses and 8,388,606 usable hosts.

CIDR prefix/9
Subnet mask255.128.0.0
Subnet mask (binary)11111111.10000000.00000000.00000000
Wildcard mask0.127.255.255
Network bits / host bits9 / 23
Total addresses8,388,608
Usable hosts8,388,606
/9 subnets in a /82

The mask ends 1 bit into octet 2, so blocks step in increments of 128 in that octet.

Try it with an address

Example /9 subnets in 10.0.0.0/8

Network First usable host Last usable host Broadcast
10.0.0.0/9 10.0.0.1 10.127.255.254 10.127.255.255
10.128.0.0/9 10.128.0.1 10.255.255.254 10.255.255.255

Frequently asked questions

What is the subnet mask for /9?

A /9 subnet mask is 255.128.0.0. In binary that is 11111111.10000000.00000000.00000000: 9 network bits followed by 23 host bits. The wildcard mask is 0.127.255.255.

How many usable hosts are in a /9?

A /9 holds 8,388,608 addresses in total. Subtracting the network and broadcast addresses leaves 8,388,606 usable hosts.

How many /9 subnets fit in a /8?

A /8 divides into 2 subnets of size /9, because each extra mask bit doubles the number of subnets.

Other prefix lengths

← /8 Full CIDR chart /10 →

Calculate this over HTTP: curl https://networkcalc.com/api/ip/192.168.1.0/9. See the Subnet Calculator API.