/20 Subnet

A /20 has 4,096 addresses, 4,094 of them usable by hosts. Its netmask is 255.255.240.0. Enter any address below to see its /20 network.

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Examples:

IPv4 network

4,094 usable hosts · 192.168.0.1 to 192.168.15.254

Private (RFC 1918)

Details

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

Split Into Subnets

192.168.0.0/21192.168.0.0 – 192.168.7.255
192.168.8.0/21192.168.8.0 – 192.168.15.255

Subnet Calculator

/20 at a glance

CIDR Prefix/20
Netmask255.255.240.0
Wildcard Mask0.0.15.255
Netmask (Hex)0xFFFFF000
Total Addresses4,096
Usable Hosts4,094
Host Bits12
Contains /24s16
Binary Mask11111111.11111111.11110000.00000000

A /20 fixes the first 20 bits of the address as the network and leaves 12 bits for hosts, so it holds 2^12 = 4,096 addresses. The first is the network address and the last is the broadcast address, leaving 4,094 for hosts.

A common allocation from regional registries to growing hosting providers and ISPs: sixteen /24s.

A /20 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 /20?
4,094. A /20 has 4,096 addresses; the network and broadcast addresses are not usable by hosts.
What is the subnet mask for /20?
255.255.240.0. The wildcard (inverse) mask, used in Cisco ACLs, is 0.0.15.255.
How many /24 networks are in a /20?
16. Each step from /20 to /24 doubles the number of networks.
Is 255.255.240.0 the same as /20?
Yes. 255.255.240.0 written in binary is 20 ones followed by 12 zeros, which is what /20 means.

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