/24 Subnet Explained: 255.255.255.0

/24 at a glance

What /24 means

The number after the slash is how many bits of the address identify the network. In a /24 the first 24 bits, which are the first three octets, are fixed for every device on the network. The last 8 bits are left for hosts, which gives 2⁸ = 256 combinations. Every device in 192.168.1.0/24 shares the prefix 192.168.1, and only the final number changes.

Of the 256 addresses, two are reserved. The first (192.168.1.0) names the network itself, and the last (192.168.1.255) is the broadcast address that reaches every host at once. That leaves 254 addresses from .1 to .254 for devices, including the router.

People still call a /24 a "Class C" network. Classful addressing was replaced by CIDR in the 1990s, so the term is only a nickname today, but it explains why /24 became the default: it lines up neatly with an octet, so it is easy to read and hard to get wrong.

A sensible layout for one /24

One common way to organize 192.168.1.0/24 on a small network is to group addresses by role, so you can recognize a device from its address alone:

• .1: the default gateway (the router or firewall).
• .2 to .9: switches, access points, and other network equipment.
• .10 to .49: static addresses for printers, servers, and cameras.
• .50 to .249: the DHCP pool for laptops and phones, 200 addresses.
• .250 to .254: spare addresses you keep for troubleshooting and future use.

Keep DHCP reservations and static addresses outside the dynamic pool, otherwise two devices can end up with the same address.

Splitting a /24 into smaller subnets

Borrowing host bits turns a /24 into several smaller networks. Each extra bit halves the size and doubles the count:

For example, one /24 can be split into four /26 networks to separate users, voice, servers, and guest Wi-Fi. The division of 192.168.1.0/24 looks like this:

You can generate and check splits like this with the subnet calculator, which also lists the full range of any prefix. Smaller blocks are covered in the /27 guide.

When a /24 is the wrong size

Too big. Every device in a /24 is in the same broadcast domain. A VLAN with 250 chatty devices generates a lot of broadcast and ARP traffic, and it is also a large blast radius if something misbehaves. A point-to-point link between two routers needs two addresses, so using a /24 there wastes 252 of them.

Too small. A busy wireless network can exhaust 254 addresses, especially with short DHCP leases and guests that reconnect often. The fix is usually a /23, which joins two adjacent /24s into a network of 510 usable hosts. The two /24s must line up: 192.168.2.0/24 and 192.168.3.0/24 combine into 192.168.2.0/23, but 192.168.1.0/24 and 192.168.2.0/24 cannot be combined into a single /23 because the first one starts at an odd number.

Checking whether two hosts share a /24

Two addresses are in the same /24 when their first three octets are identical. 192.168.1.20 and 192.168.1.200 are neighbours and can talk directly. 192.168.1.20 and 192.168.2.20 look similar, but the third octet differs, so they are in different /24 networks and need a router between them. Devices make exactly this decision by applying the mask: they AND each address with 255.255.255.0 and compare the results, sending the packet directly if the results match and to the default gateway if they do not. When a host cannot reach something that "should" be local, a wrong mask or a wrong third octet is one of the first things to check.

Common mistakes with /24 networks

• Assigning .0 or .255 to a host. In a /24 those are the network and broadcast addresses and must not be used for devices.
• Reusing the same /24 everywhere. If every branch uses 192.168.1.0/24, you cannot connect the branches over a VPN. See private IP ranges for how to avoid overlaps.
• Typing the mask wrongly on a device. A host with 255.255.0.0 on a /24 network believes the other 192.168.x.x addresses are local and will try to reach them directly instead of through the gateway.
• Leaving no spare capacity. A /24 that is 90 percent full will run out the first time you add a few devices.

Related tools and guides

Frequently asked questions