What a /28 subnet is: sixteen addresses
A /28 holds 16 addresses, 14 usable, with a block size of 16 in the last octet. It is the smallest subnet most cloud providers will let you create.
At a glance
- Subnet mask
- 255.255.255.240
- Wildcard mask
- 0.0.0.15
- Total addresses
- 16
- Usable hosts
- 14
- Block size in the last octet
- 16
- Host bits
- 4 of 32
In detail
The mask is 255.255.255.240. Fourteen usable addresses is enough for a small tier of servers and not enough for anything that scales automatically.
Common for a static block from an internet provider, and for small internal segments where the host count is genuinely fixed.
Do not use a /28 for anything with automatic scaling. When the platform reserves several addresses out of the sixteen, the effective capacity is under ten and a scale-out event fails on address exhaustion, which surfaces as a confusing quota error.
Examples
203.0.113.16/28
mask 255.255.255.240
network 203.0.113.16
broadcast 203.0.113.31
usable 203.0.113.17 to 203.0.113.30 (14 addresses)Things that catch people out
- Valid last octets are multiples of 16. 203.0.113.20/28 is not a network address.
- A public /28 from a provider usually has the gateway on the first usable address, leaving 13 for you rather than 14.
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 /29 subnet is: eight addresses
A /29 uses the mask 255.255.255.248 and gives 6 usable addresses. What it is for and where it goes wrong.
What a /27 subnet is: an eighth of a /24
A /27 uses the mask 255.255.255.224 and gives 30 usable addresses. What it is for and where it goes wrong.
What a /30 subnet is: a point-to-point link
A /30 uses the mask 255.255.255.252 and gives 2 usable addresses. What it is for and where it goes wrong.
What a /31 subnet is: a point-to-point link with no waste
A /31 uses the mask 255.255.255.254 and gives 2 usable addresses. What it is for and where it goes wrong.
What a /32 subnet is: a single host
A /32 uses the mask 255.255.255.255 and gives 1 usable addresses. What it is for and where it goes wrong.
What a /0 subnet is: the default route
A /0 uses the mask 0.0.0.0 and gives 4,294,967,294 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