# subnet mask

CEFR C1 · Compound

Source: https://englishreference.com/word/subnet-mask
Updated: 2026-07-22

## Definition

a set of numbers used in computer networking to divide a large network into smaller, manageable parts. It helps your computer figure out which other devices are on its local network and which are outside.

For teachers: a 32-bit number used to mask an IP address and divide the IP address into network address and host address bits. It identifies which portion of an IP address refers to the subnet and which refers to the device itself.

## Examples

- You need to enter the correct subnet mask to connect to the network.
- The IT technician configured the router with a subnet mask of 255.255.255.0 to ensure all office computers could communicate locally.
- By applying a custom subnet mask, network administrators can efficiently allocate IP address space and reduce unnecessary broadcast traffic across the wider corporate infrastructure.

## Usage notes

- Typically appears as a four-part number separated by dots, similar to an IP address.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.