What a /16 subnet is: a full class B block
A /16 fixes the first two octets and leaves 65,536 addresses, 65,534 of them usable. It is the standard size for a site or a cloud virtual network.
At a glance
- Subnet mask
- 255.255.0.0
- Wildcard mask
- 0.0.255.255
- Total addresses
- 65,536
- Usable hosts
- 65,534
- Contains
- 256 networks of /24
- Host bits
- 16 of 32
In detail
The mask is 255.255.0.0. Everything sharing the first two octets is on the same network, which gives a comfortable amount of room to carve into smaller subnets later.
192.168.0.0/16 is the third RFC 1918 private block. 169.254.0.0/16 is link-local, the range a host self-assigns when a DHCP server does not answer. Cloud virtual networks commonly default to a /16.
A /16 is a good allocation unit and a terrible broadcast domain. Split it into /24s or /22s per subnet. Sixty five thousand hosts sharing one layer two segment would drown in broadcast traffic long before the addresses ran out.
Examples
192.168.0.0/16 private, 192.168.0.0 to 192.168.255.255
169.254.0.0/16 link-local, self-assigned when DHCP fails
# a virtual network with room to subdivide
10.20.0.0/16 -> 10.20.1.0/24, 10.20.2.0/24, ...Things that catch people out
- An address in 169.254.0.0/16 means the host never got a DHCP lease. It is a symptom, not a configuration, and nothing outside the local link will answer it.
- 192.168.1.0/24 is a /24 inside 192.168.0.0/16, not the same thing. Home routers use the /24, which is why two home networks bridged over a virtual private network so often collide.
Try it: IP Subnet Calculator
Enter any IPv4 address with a prefix or a dotted mask and get the network address, broadcast address, wildcard mask, usable host range, address class, and the hex and binary forms.
IP Subnet Calculator
LOCAL · Browser-OnlyCalculate IP subnet details, network ranges, and CIDR notation
192.168.1.0192.168.1.255255.255.255.00.0.0.255192.168.1.0/24192.168.1.1 - 192.168.1.254192.168.1.1192.168.1.254256254C0xC0A8016411000000.10101000.00000001.01100100Split into two /25 subnets
Dividing 192.168.1.0/24 one prefix deeper.
Common Subnet Masks
Related IPv4 subnets
All ipv4 subnets →What a /24 subnet is: the classic LAN subnet
A /24 uses the mask 255.255.255.0 and gives 254 usable addresses. What it is for and where it goes wrong.
What a /8 subnet is: a full class A block
A /8 uses the mask 255.0.0.0 and gives 16,777,214 usable addresses. What it is for and where it goes wrong.
What a /22 subnet is: four /24s
A /22 uses the mask 255.255.252.0 and gives 1,022 usable addresses. What it is for and where it goes wrong.
What a /18 subnet is: a quarter of a /16
A /18 uses the mask 255.255.192.0 and gives 16,382 usable addresses. What it is for and where it goes wrong.
What a /20 subnet is: sixteen /24s
A /20 uses the mask 255.255.240.0 and gives 4,094 usable addresses. What it is for and where it goes wrong.
What a /21 subnet is: eight /24s
A /21 uses the mask 255.255.248.0 and gives 2,046 usable addresses. What it is for and where it goes wrong.
Tools for this
- IP Subnet Calculator Free online IP subnet calculator - calculate IP subnet details, CIDR notation, and network address ranges
- IP Address Lookup Free online IP address lookup - find your public IP address and basic network information
- Number Base Converter Free online number base converter - convert numbers between decimal, binary, octal, and hexadecimal