In our last module, we identified different classes of addresses. Here is the table for reference:

The address of, would be a class A address based off the first octet being 50. By default, class A networks use the first octet for the network bits. Since each octet has 8 bits, the first 8 bits would identify the network. In cider notation, this would be:

If the first 8 bits are all 1’s, the binary equivalent would be 255. Since the following bits are all host bits, the following three octets would all be set to 0. Our default subnet mask for a class A address is:

Since a class B devotes the 1st and 2nd octect, our default subnet mask would be A class C devotes the 1st, 2nd, and 3rd octet making a class C address have a default subnet mask of Here is a table for easy lookup:

Progress Check: For each of the following addresses, determine the default subnet mask. Initially, you can use the first octet and class table to determine the default subnet mask.

Check your answers with the answer key below. It’s recommended that before you proceed, you could perform this exercise without the use of the table. If you need additional practice, use the worksheet found at (link below)