The subnet mask option in networking refers to a configuration setting that defines the boundaries (or subnet) of a network segment. It is a 32-bit number typically expressed in dotted-decimal notation (e.g., 255.255.255.0) that accompanies an IP address. The subnet mask determines which portion of an IP address identifies the network and which portion identifies the host within that network. By applying the subnet mask to an IP address, devices on the network can determine whether another IP address is within the same local network segment or requires routing through a gateway to reach.
A subnet mask setting is a specific configuration applied to devices or network interfaces to define the subnet to which they belong. It is used in conjunction with IP addresses to partition a larger IP network into smaller, more manageable subnetworks (subnets). The subnet mask is essential for devices to determine whether an IP address is local to their subnet or requires forwarding to another network segment. For example, a subnet mask of 255.255.255.0 (or /24 in CIDR notation) indicates that the first three octets of an IP address are used to identify the network, while the last octet identifies individual hosts within that network.
The subnet mask and default gateway serve different purposes in networking. The subnet mask defines the boundaries of a local network segment by indicating which portion of an IP address identifies the network and which portion identifies the host. It is used by devices to determine whether another IP address belongs to the same subnet or requires routing through a gateway to reach. In contrast, the default gateway is a specific IP address assigned to devices that serves as the default route for traffic destined for destinations outside their local subnet. While the subnet mask defines internal network boundaries, the default gateway directs traffic to external networks or destinations beyond the local subnet.
IP addressing, the number 32 refers to the size of the network prefix or subnet mask applied to an IP address. Specifically, a subnet mask of 255.255.255.255 (or /32 in CIDR notation) indicates that the entire 32-bit IP address is used to identify a single host on a network. This configuration is typically used in point-to-point links or loopback interfaces where each device requires a unique, individual IP address within the same subnet. In essence, a /32 subnet mask specifies that there are no subnet bits and that the entire address space is dedicated to identifying a specific host within the network, without any additional subdivisions for network or broadcast addresses.