What is the function of a subnet mask?

• A. To encrypt an IP address
• B. To define the network and host portions of an IP address
• C. To convert IP addresses into domain names
• D. To route packets between different networks

Answer: (B)

A subnet mask serves a critical function in IP networking by defining the network and host portions of an IP address. It determines which part of the IP address identifies the specific network and which part can be used to identify individual devices (hosts) within that network. This is essential for organizing networks and managing IP address allocation efficiently.

When a device needs to communicate with another device, it uses the subnet mask to understand where the transmission should be directed. The subnet mask is used in conjunction with the IP address to facilitate communication within the same network and to differentiate between local and remote traffic.

For example, in the configuration of an IP address like 192.168.1.1 with a subnet mask of 255.255.255.0, the subnet mask allows the device to recognize that the first three octets (192.168.1) identify the network, while the last octet (1) identifies the specific device on that network. This organization simplifies routing and improves network efficiency.

Understanding the role of a subnet mask is fundamental in networking, as it influences how data packets are routed and how address space is managed within IP networks.