/12 Subnet

A /12 has 1,048,576 addresses, 1,048,574 of them usable by hosts. Its netmask is 255.240.0.0. Enter any address below to see its /12 network.

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Examples:

IPv4 network

1,048,574 usable hosts · 10.0.0.1 to 10.15.255.254

Private (RFC 1918)

Details

Netmask
Wildcard Mask
Broadcast
First Usable
Last Usable
Usable Hosts
Total Addresses
Netmask in Binary

Split Into Subnets

10.0.0.0/1310.0.0.0 – 10.7.255.255
10.8.0.0/1310.8.0.0 – 10.15.255.255

Subnet Calculator

/12 at a glance

CIDR Prefix/12
Netmask255.240.0.0
Wildcard Mask0.15.255.255
Netmask (Hex)0xFFF00000
Total Addresses1,048,576
Usable Hosts1,048,574
Host Bits20
Contains /24s4,096
Binary Mask11111111.11110000.00000000.00000000

A /12 fixes the first 12 bits of the address as the network and leaves 20 bits for hosts, so it holds 2^20 = 1,048,576 addresses. The first is the network address and the last is the broadcast address, leaving 1,048,574 for hosts.

The size of the 172.16.0.0/12 private range (172.16.0.0 to 172.31.255.255), used by Docker and many corporate networks.

A /12 can be announced in BGP on its own: /24 is the longest prefix most networks accept.

Other IPv4 Prefixes

/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32

IPv6 Prefixes

IPv6 /32IPv6 /36IPv6 /40IPv6 /44IPv6 /48IPv6 /52IPv6 /56IPv6 /60IPv6 /64IPv6 /112IPv6 /126IPv6 /127IPv6 /128

Questions

How many usable IP addresses are in a /12?
1,048,574. A /12 has 1,048,576 addresses; the network and broadcast addresses are not usable by hosts.
What is the subnet mask for /12?
255.240.0.0. The wildcard (inverse) mask, used in Cisco ACLs, is 0.15.255.255.
How many /24 networks are in a /12?
4,096. Each step from /12 to /24 doubles the number of networks.
Is 255.240.0.0 the same as /12?
Yes. 255.240.0.0 written in binary is 12 ones followed by 20 zeros, which is what /12 means.

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