Section: IT & Technology · NetworkingDifficulty: Medium
Subnet Mask
USUK
A 32-bit number that divides an IP address into network and host portions.
Also: netmask · CIDR prefix
Definition
A subnet mask is a 32-bit number used to distinguish the network portion of an IP address from the host portion, enabling routers to determine whether traffic should stay on the local network or be forwarded to another network. Written in dotted-decimal notation (e.g., 255.255.255.0) or CIDR notation (e.g., /24), subnetting allows network administrators to divide large networks into smaller, more manageable segments, improving security and performance.
Example
“With a subnet mask of 255.255.255.0, all devices with IP addresses 192.168.1.1 through 192.168.1.254 are on the same local network.”
Synonyms
- network mask
- CIDR notation
- netmask
- subnet prefix
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Related Terms
- ip-address
- cidr
- subnetting
- router