What is a /28 subnet? 16 IPs for small server groups and point-to-point links
A /28 is the smallest subnet you should provision for anything that might grow. It gives 14 generic IPv4 host addresses, or 11 assignable addresses in AWS and Azure after their five-address reservation. That can cover a small server group plus a few spares, but choose a larger cloud subnet when the growth plan needs more room. For point-to-point links where you need exactly 2 addresses, use a /30 or /31 instead.
A /28 subnet, written as 255.255.255.240, provides 16 total addresses with 14 usable on a conventional IPv4 subnet. AWS and Azure reserve five addresses in each subnet, leaving 11 assignable addresses there. This is a compact size for small server groups, DMZ segments, and cloud subnets where you need isolation without wasting address space.
By TechCompare · Updated
How this is calculated
With 14 generic IPv4 host addresses, a /28 fits a small cluster of web servers, a database HA pair with monitoring, or a dedicated management network. Cloud providers like AWS and Azure let you create /28 subnets within a VPC or VNet, but both reserve the first four and last addresses, leaving 11 assignable addresses. The subnet mask 255.255.255.240 means each /28 block increments the last octet by 16 (e.g., .0-.15, .16-.31, .32-.47).
Verdict
The /28 mask 255.255.255.240 reserves 28 bits for the network and leaves 4 bits for hosts, which is 16 total addresses minus the traditional network and broadcast reservations, leaving 14 usable on a conventional IPv4 subnet. Each /28 block increments the last octet by 16 (.0-.15, .16-.31, .32-.47). AWS and Azure reserve five addresses instead, so only 11 are assignable in those environments. That is enough for a small cloud service group in some designs, but the growth case should be based on 11 rather than 14. For a true point-to-point router link that only needs 2 addresses, drop to a /30 or /31 to save the wasted space.
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Frequently asked questions
How many usable hosts in a /28?
How many usable IPs are in a /28?
When should I use a /28 instead of a /30?
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