CompTIA Network+ Practice Test

What is a subnet mask used for in IPv4 addressing?

1. A 32-bit number that identifies the subnet a device belongs to

2. A unique identifier for devices on the internet

3. The physical address of a device on a network

4. An alternative address format for private networks

The correct answer is: A 32-bit number that identifies the subnet a device belongs to

A subnet mask plays a crucial role in IPv4 addressing by defining the network and host portions of an IP address. It is a 32-bit number that is used in conjunction with an IPv4 address to determine which part of the address refers to the network and which part refers to the individual device (or host) within that network. For example, if an IP address is 192.168.1.10 and the subnet mask is 255.255.255.0, the subnet mask indicates that the first three octets (192.168.1) are designated for the network, while the last octet is used for host addresses within that network. This allows devices on the same subnet to communicate directly with each other without needing to go through a router, optimizing network performance and organization. Other options do not accurately reflect the function of a subnet mask. A unique identifier for devices on the internet is typically represented by an IP address itself, while the physical address of a device on a network refers to a MAC address. An alternative address format for private networks does not relate to the definition or purpose of a subnet mask in IPv4 addressing.