What is the default subnet mask typically used in IPv4 addresses?

The default subnet mask is a key concept in networking, particularly for IPv4 addresses. A subnet mask is used to determine which portion of an IP address is the network address and which portion can be used for hosts within that network.

In the case of the choice provided, the default subnet mask of 255.255.255.0 is commonly used for Class C addresses, which include IP addresses ranging from 192.0.0.0 to 223.255.255.255. This mask allows for a maximum of 256 IP addresses (from 0 to 255), with 254 usable addresses for hosts, as two addresses are reserved (the network and broadcast addresses).

The other options, although they represent valid IP addresses or subnet masks, do not serve as the default subnet mask for commonly used IPv4 classes. For example, the address 255.0.0.0 is a Class A default subnet mask, which applies to a much larger address range. Likewise, 128.0.0.1 is an example of an IP address rather than a subnet mask, and 192.168.1.1 is a specific host address, not a subnet mask.

Thus, 255.255.255.0