• A: size 70
• B: size 40
• C: size 25
• D: size 20

We get to our site using the first three bytes of the /24 IPv4 address. Now we want to route to A, B, C or D using only a prefix of the fourth byte. The use of prefixes means that each subnet size will be a power of 2. (Could we, in theory or in practice, divide into ranges by numeric intervals, [1..70], [71..110], [111-135], [136..155]? How would you then handle overlaps?)

Step one: round up to powers of 2

Step 2: figure out how many prefix bits (subnet bits) we have for each: 1 for A, 2 for B, 3 for C and D

Step 3: Start filling them in!

A:    ____

B:    ____   ____

C:    ____   ____   ____

D:    ____   ____   ____