The main difference between IPv4 and IPv6 addresses lies in their format and capacity. IPv4, the older protocol, utilizes a 32-bit address scheme, allowing for approximately 4.3 billion unique IP addresses. In contrast, IPv6 employs a 128-bit address scheme, vastly increasing the number of available addresses to approximately 340 undecillion. This upgrade addresses the scarcity of IPv4 addresses due to the explosive growth of the internet. Additionally, IPv6 includes features like simplified routing, built-in security, and improved support for modern devices.