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/9 Subnet Mask: 255.128.0.0

A /9 prefix fixes the first 9 bits of the address as the network, leaving 23 bits for hosts. That gives 8,388,608 addresses, of which 8,388,606 can be assigned to hosts.

CIDR notation/9
Subnet mask255.128.0.0
Wildcard mask0.127.255.255
Binary mask11111111.10000000.00000000.00000000
Hex mask0xFF800000
Total addresses8,388,608
Usable hosts8,388,606

Example: 10.0.0.0/9

  • Network address: 10.0.0.0
  • First usable host: 10.0.0.1
  • Last usable host: 10.127.255.254
  • Broadcast address: 10.127.255.255

When to use a /9 subnet

Very large private networks. 10.0.0.0/8 is the largest private IPv4 range defined by RFC 1918.

  • 2 /9 subnets fit in a /8.

Frequently Asked Questions

What is the subnet mask for /9?

The subnet mask for /9 is 255.128.0.0, and its wildcard (inverse) mask is 0.127.255.255.

How many hosts are in a /9?

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