Because IPv4 uses only 32 bits for its IP addresses (called its address space), the number of total unique IP addresses is limited. IPv4 addresses are four numbers, separated by dots. Each number can only be up to 256. One example of an IPv4 address is 126.96.36.199. When the Internet was first designed, its creators never imagined that the address space would ever fill up, which is why they designed it the way they did.