CIDR prefix
/1
128.0.0.0
2,147,483,646 usable hosts · 2,147,483,648 addresses
The mask for /1 is 128.0.0.0 — 2,147,483,648 addresses, 2,147,483,646 usable hosts. Huge blocks used only by registries and carriers.
Mask
128.0.0.0
Wildcard
127.255.255.255
Addresses
2,147,483,648
Hosts
2,147,483,646
Worked example: 10.0.0.0/1
Network address0.0.0.0/1
Broadcast address127.255.255.255
First host0.0.0.1
Last host127.255.255.254
FAQ — /1
What is the subnet mask for /1?
The subnet mask for /1 is 128.0.0.0 (wildcard: 127.255.255.255). The first 1 bits are the network part, the remaining 31 are the host part.
How many hosts fit in a /1?
A /1 block holds 2,147,483,648 addresses, of which 2,147,483,646 are usable hosts (the network and broadcast addresses are excluded).
What is a /1 used for?
Huge blocks used only by registries and carriers.