/18 Subnet

A /18 has 16,384 addresses, 16,382 of them usable by hosts. Its netmask is 255.255.192.0. Enter any address below to see its /18 network.

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Examples:

IPv4 network

16,382 usable hosts · 192.168.0.1 to 192.168.63.254

Private (RFC 1918)

Details

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

Split Into Subnets

192.168.0.0/19192.168.0.0 – 192.168.31.255
192.168.32.0/19192.168.32.0 – 192.168.63.255

Subnet Calculator

/18 at a glance

CIDR Prefix/18
Netmask255.255.192.0
Wildcard Mask0.0.63.255
Netmask (Hex)0xFFFFC000
Total Addresses16,384
Usable Hosts16,382
Host Bits14
Contains /24s64
Binary Mask11111111.11111111.11000000.00000000

A /18 fixes the first 18 bits of the address as the network and leaves 14 bits for hosts, so it holds 2^14 = 16,384 addresses. The first is the network address and the last is the broadcast address, leaving 16,382 for hosts.

A /18 is 64 /24 networks side by side; registries and ISPs allocate blocks this size to networks that route them on the internet.

A /18 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 /18?
16,382. A /18 has 16,384 addresses; the network and broadcast addresses are not usable by hosts.
What is the subnet mask for /18?
255.255.192.0. The wildcard (inverse) mask, used in Cisco ACLs, is 0.0.63.255.
How many /24 networks are in a /18?
64. Each step from /18 to /24 doubles the number of networks.
Is 255.255.192.0 the same as /18?
Yes. 255.255.192.0 written in binary is 18 ones followed by 14 zeros, which is what /18 means.

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