/2 Subnet Mask ReferenceIPv4
Fix the top two bits and one quarter of IPv4, some 1,073,741,824 addresses, collapses into a single /2 behind mask <code>192.0.0.0</code>. Its best party trick is historical: the old Class C, D, and E ranges together fill exactly one /2.
/2 facts at a glance
- Subnet mask
- 192.0.0.0
- Wildcard mask
- 63.255.255.255
- Binary mask
- 11000000.00000000.00000000.00000000
- Total addresses
- 1,073,741,824
- Usable hosts
- 1,073,741,822 (excludes network & broadcast)
- Block size
- 1,073,741,824 addresses (230)
- Typical role
- Aggregation and supernetting
Example /2 networks
A /2 spans a large share of the address space, so one aligned example says it all.
| Network | Usable range | Usable hosts |
|---|---|---|
| 192.0.0.0/2 | 192.0.0.1 – 255.255.255.254 | 1,073,741,822 |
How to calculate a /2 mask
A /2 mask sets the first 2 bits of a 32-bit number to 1 and leaves the remaining 30 bits as 0. In binary that reads 11000000.00000000.00000000.00000000, which converts to dotted decimal 192.0.0.0. Each block covers a contiguous run of 230 = 1,073,741,824 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 63.255.255.255.
Where /2 is used
- CIDR hierarchy lessons: four /2 blocks tile the whole address space.
- Aggregation arithmetic practice with very large blocks.
- Understanding how the legacy classful map sits inside modern CIDR.
The block <code>192.0.0.0/2</code> runs from 192.0.0.0 through 255.255.255.255, sweeping up former Class C (192-223), multicast Class D (224-239), and reserved Class E (240-255) in one stroke.
Frequently asked questions
What is the subnet mask for a /2?
<code>192.0.0.0</code>; the wildcard is <code>63.255.255.255</code>. Two leading one-bits leave 30 host bits.
How many addresses does a /2 contain?
1,073,741,824 total, with 1,073,741,822 usable under the usual network-and-broadcast convention.
How many /8 networks fit in a /2?
Four. A /2 groups eight first-octet values, and each /8 consumes two of them.
Open this block in a calculator
Open the /2 block in the subnet calculator