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/16 Subnet Mask: 255.255.0.0

A /16 prefix fixes the first 16 bits of the address as the network, leaving 16 bits for hosts. That gives 65,536 addresses, of which 65,534 can be assigned to hosts. Before CIDR, /16 was the default mask of a Class B network.

CIDR notation/16
Subnet mask255.255.0.0
Wildcard mask0.0.255.255
Binary mask11111111.11111111.00000000.00000000
Hex mask0xFFFF0000
Total addresses65,536
Usable hosts65,534

Example: 172.16.0.0/16

  • Network address: 172.16.0.0
  • First usable host: 172.16.0.1
  • Last usable host: 172.16.255.254
  • Broadcast address: 172.16.255.255

When to use a /16 subnet

Entire VPCs or campus networks. /16 is the largest CIDR block AWS allows for a VPC.

  • 256 /16 subnets fit in a /8.

Frequently Asked Questions

What is the subnet mask for /16?

The subnet mask for /16 is 255.255.0.0, and its wildcard (inverse) mask is 0.0.255.255.

How many hosts are in a /16?

A /16 contains 65,536 addresses. Subtracting the network and broadcast addresses leaves 65,534 usable hosts.