IPv4 and its limits

First defined in 1981, and widely deployed in 1983, IPv4 has been the standard for network layer interactions across the whole of the internet, and almost every local area network, for over three decades now. As I mentioned before, nearly 80% of all internet traffic is done using the IPv4 specification of the IP interface. Its stability, scalability, and reliability have been well-proven at this point. So, what is it about IPv4 that made its implementation of network layer responsibilities so successful? And what was it about the IPv4 specification that precipitated the need, after such a long and successful lifespan, to define and deploy a new protocol with IPv6?

The addressing standard of IPv4

As I mentioned...