/16 Subnet

A /16 has 65,536 addresses, 65,534 of them usable by hosts. Its netmask is 255.255.0.0. Enter any address below to see its /16 network.

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Examples:

IPv4 network

65,534 usable hosts · 192.168.0.1 to 192.168.255.254

Private (RFC 1918)

Details

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

Split Into Subnets

192.168.0.0/17192.168.0.0 – 192.168.127.255
192.168.128.0/17192.168.128.0 – 192.168.255.255

Subnet Calculator

/16 at a glance

CIDR Prefix/16
Netmask255.255.0.0
Wildcard Mask0.0.255.255
Netmask (Hex)0xFFFF0000
Total Addresses65,536
Usable Hosts65,534
Host Bits16
Contains /24s256
Binary Mask11111111.11111111.00000000.00000000

A /16 fixes the first 16 bits of the address as the network and leaves 16 bits for hosts, so it holds 2^16 = 65,536 addresses. The first is the network address and the last is the broadcast address, leaving 65,534 for hosts.

The old Class B size. 192.168.0.0/16 is a private range; on the public internet a /16 is a large allocation for a big ISP or cloud.

A /16 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 /16?
65,534. A /16 has 65,536 addresses; the network and broadcast addresses are not usable by hosts.
What is the subnet mask for /16?
255.255.0.0. The wildcard (inverse) mask, used in Cisco ACLs, is 0.0.255.255.
How many /24 networks are in a /16?
256. Each step from /16 to /24 doubles the number of networks.
Is 255.255.0.0 the same as /16?
Yes. 255.255.0.0 written in binary is 16 ones followed by 16 zeros, which is what /16 means.

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