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Network prefix

(also network mask, subnet mask)

Network prefix definition

A network prefix is a number that identifies the network portion of an IP address. It helps devices decide if an IP address is on the same network or needs to be sent elsewhere.

The prefix is shown as a number after a slash, like “/24,“ which tells how many bits are used for the network. A shorter prefix gives more addresses to devices but fewer networks, while a longer prefix gives more networks but fewer addresses.

See also: Network ID, Next hop

Network prefix use cases

  • Determining Network Membership. Network prefixes help devices determine if an IP address belongs to the same network or a different one for communication.
  • Routing Decision. Devices compare network prefixes to decide whether to send data directly to a device on the local network or route it to another network.
  • Subnetting. Network prefixes divide big networks into smaller ones called subnets, making it easier to manage and assign IP addresses within an organization.
  • Security and Access Control. Prefixes help define specific networks or subnets that are allowed or denied access to certain resources or services, improving security.
  • Network Address Translation (NAT). NAT maps multiple private IP addresses to a single public IP address. Network prefixes determine which IP addresses should be translated when connecting with external networks.
  • IP Address Planning. Network prefixes assist in planning and organizing IP address ranges for different networks. Prefixes ensure efficient use of available addresses when setting up networks.