/1 Subnet Mask (128.0.0.0)
| Prefix | /1 |
|---|---|
| Subnet mask | 128.0.0.0 |
| Wildcard mask | 127.255.255.255 |
| Binary mask | 10000000.00000000.00000000.00000000 |
| Total addresses | 2,147,483,648 |
| Usable hosts | 2,147,483,646 |
| Host bits | 31 |
| Subnets of /1 in a /0 | 2 |
e.g. 10.0.0.5/22 or 10.0.0.5 255.255.252.0
| Network address | 0.0.0.0 | |
|---|---|---|
| Broadcast address | 127.255.255.255 | |
| First usable host | 0.0.0.1 | |
| Last usable host | 127.255.255.254 | |
| Total addresses | 2,147,483,648 | |
| Usable hosts | 2,147,483,646 | |
| Subnet mask | 128.0.0.0 | |
| Wildcard mask | 127.255.255.255 | |
| CIDR notation | 0.0.0.0/1 | |
| IP class | Class A (legacy) | |
| Address type | "This network" (RFC 1122) | |
| IP address (binary) | 00000000.00000000.00000000.00000000 | |
| Subnet mask (binary) | 10000000.00000000.00000000.00000000 |
■ network bits ■ host bits
| Requested hosts | CIDR | First host | Last host | Broadcast | Usable hosts |
|---|
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What is a /1 subnet?
A /1 subnet uses the first 1 bits of an IPv4 address for the network and leaves 31 bits for hosts. Its subnet mask is 128.0.0.0, and it contains 2³¹ = 2,147,483,648 addresses, of which 2,147,483,646 can be assigned to devices. Typical use: Very large blocks only seen in routing tables and IANA allocations; /4 is the multicast range 224.0.0.0/4. Use the subnet calculator above to check any /1 network.
A /1 covers 1/2 of the IPv4 address space (2³¹ of 2³² addresses).
/1 subnet example
For 0.0.0.0/1: network address 0.0.0.0, usable hosts 0.0.0.1 – 127.255.255.254, broadcast address 127.255.255.255, wildcard mask 127.255.255.255.
Frequently asked questions
How many usable IPs are in a /1?
2,147,483,646. The block has 2,147,483,648 addresses; the first is the network address and the last is the broadcast address.
What is the subnet mask for /1?
128.0.0.0, or 10000000.00000000.00000000.00000000 in binary.
How many /1 subnets are in a /0?
2 (2¹), because a /1 uses 1 more network bits than a /0.
What is the difference between /1 and /0?
A /0 (0.0.0.0) is twice as large: 4,294,967,296 addresses and 4,294,967,294 usable hosts, spanning two consecutive /1 blocks such as 0.0.0.0–255.255.255.255.