IPv4 subnetting can look intimidating at first, but a /28 subnet is one of the easiest CIDR blocks to understand once the basic math is clear. In practical networking, a /28 is often used for small office networks, lab environments, static public IP assignments, firewall segments, and small groups of servers that need their own address range.
TLDR: A /28 subnet contains 16 total IP addresses. In a standard IPv4 network, 14 addresses are usable because one address is reserved as the network address and one is reserved as the broadcast address. CIDR notation, such as /28, shows how many bits are used for the network portion of an IP address. The smaller the number after the slash, the larger the subnet; the larger the number, the smaller the subnet.
What Does /28 Mean?
CIDR stands for Classless Inter-Domain Routing. It replaced the older class-based IP system and allows networks to be divided more flexibly. Instead of saying an address belongs to Class A, B, or C, CIDR uses a slash followed by a number, such as /24, /28, or /30.
IPv4 addresses are made of 32 bits. The CIDR number tells how many of those bits are used to identify the network. Therefore, in a /28 subnet, the first 28 bits identify the network, and the remaining 4 bits are available for host addresses.
The number of available addresses is calculated with this formula:
2host bits = total addresses
For a /28 subnet, there are 4 host bits:
24 = 16 total IP addresses
How Many Usable IP Addresses Are in a /28?
A /28 subnet has 16 total IP addresses, but not all of them are normally assigned to devices. In traditional IPv4 subnetting, two addresses are reserved:
- Network address: Identifies the subnet itself.
- Broadcast address: Sends traffic to all hosts within the subnet.
Because of these reservations, the usual number of usable IP addresses is:
16 total addresses − 2 reserved addresses = 14 usable addresses
So, the direct answer is: a /28 subnet contains 16 total IP addresses and 14 usable host addresses.
Example of a /28 Subnet
Consider the network 192.168.1.0/28. This subnet includes the following address range:
| Address Type | IP Address |
|---|---|
| Network address | 192.168.1.0 |
| First usable address | 192.168.1.1 |
| Last usable address | 192.168.1.14 |
| Broadcast address | 192.168.1.15 |
In this example, addresses from 192.168.1.1 through 192.168.1.14 can usually be assigned to routers, servers, workstations, printers, access points, or other network devices.
Subnet Mask for a /28
The subnet mask for a /28 is:
255.255.255.240
This mask shows that the first 28 bits are set to 1, representing the network portion. The remaining 4 bits are set to 0, representing the host portion. In binary, the final octet of 240 is:
11110000
The first four bits in that octet belong to the network, and the last four bits are used for host addresses. Since four host bits remain, the subnet contains 16 total addresses.
How /28 Subnets Increment
A useful way to understand /28 networks is to look at their block size. Since a /28 has 16 addresses, each subnet begins every 16 addresses in the final octet.
For example, within the 192.168.1.0/24 range, the /28 subnets would begin like this:
- 192.168.1.0/28 — addresses 192.168.1.0 to 192.168.1.15
- 192.168.1.16/28 — addresses 192.168.1.16 to 192.168.1.31
- 192.168.1.32/28 — addresses 192.168.1.32 to 192.168.1.47
- 192.168.1.48/28 — addresses 192.168.1.48 to 192.168.1.63
This pattern continues in increments of 16. Recognizing this increment helps network engineers quickly identify the network address, broadcast address, and usable IP range.
Image not found in postmetaWhy Would a Network Use a /28?
A /28 subnet is useful when a network needs a small but practical number of IP addresses. It is larger than a /30, which is commonly used for point-to-point links, but smaller than a /27 or /24. This makes it a good fit for compact network segments.
Common uses for a /28 include:
- Small business networks with a limited number of devices.
- Public IP allocations from an internet service provider.
- Server groups that need dedicated public or private addresses.
- Firewall DMZ networks for hosting web, mail, or VPN services.
- Testing labs where a small, isolated subnet is required.
For example, an organization may receive a public /28 block from its ISP. That gives it 16 total public IPv4 addresses, with 14 typically usable. Those addresses might be assigned to a firewall, load balancer, VPN gateway, mail server, web server, monitoring system, and several spare services.
Comparing /28 with Other CIDR Blocks
The relationship between CIDR size and available addresses becomes clearer when /28 is compared with nearby subnet sizes:
| CIDR Block | Total Addresses | Usable Addresses | Subnet Mask |
|---|---|---|---|
| /24 | 256 | 254 | 255.255.255.0 |
| /27 | 32 | 30 | 255.255.255.224 |
| /28 | 16 | 14 | 255.255.255.240 |
| /29 | 8 | 6 | 255.255.255.248 |
| /30 | 4 | 2 | 255.255.255.252 |
As the CIDR prefix gets larger, the subnet gets smaller. A /29 has fewer addresses than a /28, while a /27 has more. This is because a larger CIDR prefix leaves fewer bits for hosts.
How to Calculate a /28 Quickly
There are several quick steps an administrator can use to calculate a /28 subnet:
- Start with the total IPv4 bit length: 32 bits.
- Subtract the CIDR prefix: 32 − 28 = 4 host bits.
- Calculate total addresses: 24 = 16.
- Subtract the network and broadcast addresses: 16 − 2 = 14 usable.
This same method works with most IPv4 CIDR blocks. For example, a /29 leaves 3 host bits, so it has 8 total addresses. A /27 leaves 5 host bits, so it has 32 total addresses.
Important Notes About Usable Addresses
In most standard IPv4 LAN and routed subnet designs, the first address is treated as the network address and the last address is treated as the broadcast address. That is why a /28 normally provides 14 usable host IPs.
However, networking behavior can vary in specialized environments. Some cloud providers, for example, reserve additional addresses inside a subnet for platform services. In those cases, the number of addresses available to customers may be less than 14. Documentation from the specific provider or network platform should always be checked.
FAQ
- How many IP addresses are in a /28 subnet?
- A /28 subnet contains 16 total IPv4 addresses.
- How many usable hosts are in a /28?
- In standard IPv4 subnetting, a /28 provides 14 usable host addresses, because the network and broadcast addresses are reserved.
- What is the subnet mask for /28?
- The subnet mask for a /28 is 255.255.255.240.
- What is an example of a /28 range?
- An example is 192.168.1.0/28, which includes 192.168.1.0 through 192.168.1.15, with 192.168.1.1 through 192.168.1.14 normally usable.
- Is a /28 bigger than a /29?
- Yes. A /28 has 16 total addresses, while a /29 has 8 total addresses.
- When should a /28 subnet be used?
- A /28 is suitable for small networks, public IP blocks, DMZ segments, server groups, and lab environments that need around 14 usable IPv4 addresses.
