When IPV4 was created in the early 1970s, it was created to build a defense department network. No one foresaw the that the Internet as we know it today was going to happen. The creators did not foresee it ballooning into the largest network in the world. As address space was handed out without the thought of space running out, routers received very large route tables to handle. Routers were small and slow and became overloaded. Solutions like VLSM capable protocols and NAT came into the picture to reassign and redistribute addresses. IPV4 continued to function until Europe and Asia realized that mathematically IPV4 would not last. This is where IPV6 comes in. IPV4 is a 32 bit string providing 4 billion addresses. IPV6 is a 128 bit string providing 500,000,000,000,000,000,000,000,000,000 addresses for each person on the planet.
ICANN has the overall responsibility of distributing the IPV6 address space. They do so with the understanding of global demand for IPV6 addresses. It works like this if you think of the internet as a tree with branches. Each router is responsible for its own branch of its tree with other branches feeding into it. ARIN was given the block of 2620:000::/23 in September of 2006. It is a core router that advertises “I can reach all routers in North America”. That router talks to the ISP routers. Each ISP router connects to smaller ISP routers. Each of those routers connects to smaller routers or large enterprise routers who represent the address space assigned to them. Changes at or below the ISP level does not affect the global routing information at the core.
For hosts to use IPV6, an IPV6 protocol stack must be installed. This means that routers, computers, printers, etc. must be upgraded to provide IPV6 support in order for IPV6 to work. The device must be able to both send and receive IPV4 and IPV6 packets on the same interface. A drawback is the additional load on the device or incompatibility of the device. The process of transiting to IPV6 is not going to occur overnight. Most modern computers have the IPV6 protocol stack installed. Most modern routers have the IPV6 protocol stack installed.
The core routers are ready for IPV6. Modern devices are ready for IPV6. However, according to Cisco, there are routers on the Internet tree, if you go back to the analogy of the tree, that are not yet upgraded. Hence, the Internet is not ready to completely transition to IPV6.