What is a /12 subnet?
1,048,574 usable hosts out of 1,048,576 addresses, behind netmask 255.240.0.0.
| Prefix | /12 |
|---|---|
| Netmask | 255.240.0.0 |
| Wildcard | 0.15.255.255 |
| Total addresses | 1,048,576 |
| Usable hosts | 1,048,574 |
| Example block | 10.0.0.0/12 |
| Usable host range | 10.0.0.1 – 10.15.255.254 |
| Broadcast | 10.15.255.255 |
A /12 fixes the first 12 bits of the address as the network and leaves 20 for hosts — 1,048,576 addresses in all.
Of those, 1,048,574 can be given to a machine: the first address names the network itself, and the last is the broadcast address.
A block this large is an allocation rather than a subnet — a whole private range to carve up, or something a regional registry hands out. You would not put hosts directly in it.
It is 4,096 times the size of a /24.
Other subnet sizes
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