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/1 Subnet Mask: 128.0.0.0

A /1 prefix fixes the first 1 bits of the address as the network, leaving 31 bits for hosts. That gives 2,147,483,648 addresses, of which 2,147,483,646 can be assigned to hosts.

CIDR notation/1
Subnet mask128.0.0.0
Wildcard mask127.255.255.255
Binary mask10000000.00000000.00000000.00000000
Hex mask0x80000000
Total addresses2,147,483,648
Usable hosts2,147,483,646

Example: 0.0.0.0/1

  • Network address: 0.0.0.0
  • First usable host: 0.0.0.1
  • Last usable host: 127.255.255.254
  • Broadcast address: 127.255.255.255

When to use a /1 subnet

Huge address blocks allocated to regional internet registries and large organizations; rarely used for subnetting.

Frequently Asked Questions

What is the subnet mask for /1?

The subnet mask for /1 is 128.0.0.0, and its wildcard (inverse) mask is 127.255.255.255.

How many hosts are in a /1?

A /1 contains 2,147,483,648 addresses. Subtracting the network and broadcast addresses leaves 2,147,483,646 usable hosts.