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Troubleshooting

What Is a Subnet Mask? (Plain English Explanation)

A subnet mask tells your device which IP addresses are on the same local network and which need to go via the router. Here's what it means in practice.

Updated 2026

  1. 1

    What a subnet mask looks like

    The most common home network subnet mask is 255.255.255.0. You'll see it in network settings alongside your IP address.

  2. 2

    What it means

    255.255.255.0 means the first three numbers of your IP (e.g. 192.168.1) identify your network, and the last number identifies your device. All devices sharing 192.168.1.x are on the same local network.

  3. 3

    Why it matters

    Your device uses the subnet mask to decide: is this destination on my local network (send directly) or on the internet (send to the router)? Getting it wrong breaks network connectivity.

  4. 4

    When you'll encounter it

    Mostly during manual IP configuration — setting a static IP on a device, configuring a server, or troubleshooting connectivity. For DHCP networks it's set automatically.

Frequently Asked Questions

What does /24 mean in network notation?
/24 is shorthand for 255.255.255.0 — it means 24 bits are used for the network address. Common alternatives: /16 (255.255.0.0) for larger networks, /8 (255.0.0.0) for very large ones.
Do I ever need to change the subnet mask?
Almost never on a home network. The default 255.255.255.0 is correct for virtually all home setups.