/12 subnet (255.240.0.0)
A /12 network has 1,048,576 addresses, of which 1,048,574 can be given to hosts after the network and broadcast addresses. A very large block, typically an ISP or regional allocation, or a carved-up part of 10.0.0.0/8.
- CIDR notation
- /12
- Subnet mask
- 255.240.0.0
- Wildcard mask
- 0.15.255.255
- Binary mask
- 11111111.11110000.00000000.00000000
- Total addresses
- 1,048,576
- Usable hosts
- 1,048,574
- Example network
- 10.0.0.0/12
- Example usable range
- 10.0.0.1 – 10.15.255.254
- /24 networks in a /12
- 4,096
Calculate a /12 for your own address
In firewall rules and investigations
A /12 rule matches every address from 10.0.0.0 to 10.15.255.255. In Cisco ACLs the same range is written with the wildcard mask 0.15.255.255. When an alert names an IP, checking whether it falls inside a known /12 (your own network, a cloud provider’s published range or a blocked range) is often the quickest first step.