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/18 Subnet Mask: 255.255.192.0

A /18 prefix fixes the first 18 bits of the address as the network, leaving 14 bits for hosts. That gives 16,384 addresses, of which 16,382 can be assigned to hosts.

CIDR notation/18
Subnet mask255.255.192.0
Wildcard mask0.0.63.255
Binary mask11111111.11111111.11000000.00000000
Hex mask0xFFFFC000
Total addresses16,384
Usable hosts16,382

Example: 172.16.0.0/18

  • Network address: 172.16.0.0
  • First usable host: 172.16.0.1
  • Last usable host: 172.16.63.254
  • Broadcast address: 172.16.63.255

When to use a /18 subnet

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

  • 1,024 /18 subnets fit in a /8.
  • 4 /18 subnets fit in a /16.

Frequently Asked Questions

What is the subnet mask for /18?

The subnet mask for /18 is 255.255.192.0, and its wildcard (inverse) mask is 0.0.63.255.

How many hosts are in a /18?

A /18 contains 16,384 addresses. Subtracting the network and broadcast addresses leaves 16,382 usable hosts.