First of all, what the heck happened with IPV4? That’s a long story. IPV4 has been around since forever. Or at least it seems like that. It has been in widespread use since 1981 when computers were rare, big, and expensive. It had provision for 4 billion IP addresses, which seemed like an enormous amount at the time.
What’s Wrong with IPV4?
The first problem was that IP addresses are not used consequently and there are gaps in the addressing. That means some of that 4 billion is just wasted space. Today that big number doesn’t seem so big.
People recognized that this was a problem in the early 1990s and started coming up with solutions. Two of those were Classless Internet Domain Router (CIDR) and private IP addresses. These two solutions helped prevent an immediate disaster, but they were only stopgap measures and the problems continued. Those continuing problems included the fact that the IPV4 header was of variable length. That was okay when routing was done by software, but now routers are built with hardware, and processing the variable length headers in hardware is hard. Large routers were having large problems with IPV4.
There were more problems with IPV4 including that when the addresses were allocated, the internet was an American invention but around the world IP addresses are fragmented. In addition, IPV4, is still hard to configure, and hard to change. But something had to change.
That was the move to IPV6. It was called 6, because the number 5 was allocated to something else by mistake. But this new version had several main improvements. They included a 128-bit address system, a scheme for logically aggregating addresses. fixed length headers, and a protocol for automatically configuring and reconfiguring your network. The addresses are so big because the designers were concerned about the inefficient organization of addresses, and they built the system bigger so that people could add on their own details. That included building their own IPV6 networks and add on as many subnets that they wanted.
With aggregation, this allowed ISPs and organizations to go as big or as small as they wanted. For example, if an ISP gets a network space of 80 bits, 16 of them are for the ISPs subnetworks, and 64 bits are for the customer’s networks. So, the ISP can have 65,534 networks. That works better for everybody. In addition, this address allocation isn’t cast in stone, and if the ISP wants more smaller networks, it can do that and the system even allows the networks to be aggregated in the routing tables.
Benefits of IPV6
Fixed length headers changed the system from when the IPV4 headers had a variable length. This consistency stopped the problems created when the old system automatically caused the header to increase in size. Now additional information is stored in extension headers, which follow the IPV6 header and are generally not processed by the routers, but rather by the software at the destination. This feature makes IPV6 very easy to route.
Automatic configuration is another great improvement with IPV6. Now, when a machine first starts up, it checks the local network to see if any other machine is using its address. If the address is unused, then the machine next looks for an IPV6 router on the local network. If it finds the router, then it asks the router for an IPV6 address to use. Now, the machine is set and ready to communicate on the internet. It has an IP address for itself and it has a default router. If the router goes down, the machines on the network will detect the problem and repeat the process of looking for an IPV6 router, to find the backup router. That’s a major improvement over the old system.