The number of available IPv4 addresses is limited due to several factors, including:

• Lack of address space: The number of different devices connected to the internet grows exponentially, and the size of the address space is quickly depleted.

• Weak protocol extensibility: The insufficient size of the IPv4 header does not accommodate the required number of additional parameters.

• Geographic limitations: Since the internet was created in the USA, this country is also involved in the distribution of IP addresses. Almost 50% of all addresses are reserved for the United States.

• Issues with NAT: Network Address Translation (NAT) is a technique used to allow multiple devices to share a single public IP address. However, it can cause issues with certain applications and protocols.

• Port number limitations: Because of the port numbers, the number of connections one IP address can establish to a certain server at the same time is limited to about 60,000.

IPv4 exhaustion is the depletion of the pool of unallocated IPv4 addresses. The original internet architecture had fewer than 4.3 billion addresses available, and depletion has been aggravated by several driving factors, including mobile devices and unanticipated demand on the limited supply of addresses. IPv6 was designed to address this problem and supports approximately 3.4×10^38 network addresses.