Each device at a customer premise that connects to the internet must have an IP address. In the process of ordering a circuit a customer must request IP address space. These requests ultimately go through ARIN but are processed on behalf of the customer by the carrier. Customers must justify the amount of IP address space that they will need according to the number of customers_ amount of business_ projected growth_ how the addresses will be used_ etc. ARIN allocates IP addresses on a 3-month timeline_ meaning that customers must request only the amount of IP addresses that they will need within the next 3 months.
The following classifications exist for IP block allocations:
Class A addresses are for large networks with many devices. (Tier 1 Carriers)
Class B addresses are for medium-sized networks. (Regional Carriers and Fortune 100 companies)
Class C addresses are for small networks (fewer than 256 devices - most businesses).
Class D addresses are multicast addres