 The IP protocol that we have so far been talking about was the fourth version of its kind that saw tremendous appreciation, deployment and success all over the world. But as it is said, there is always an end to everything. The internet protocol version 4 actually had certain limitations which make it inept to be deployed in today's settings. It is already being replaced with its advanced version called IP version 6. In this module, we'll quickly look at IP version 6 as a contender to be executed and utilized at the network layer for next generation networks. The IP version 6 is meant to address a number of problems. One of the most important problems that made the scientific community think to look for the alternatives to IP version 4 was the ROADS problem. ROADS here implies the running out address space. Since the IP version 4 addresses are based on classful addressing such as A, B, C and D, there was a requirement to make it more flexible so classless inter-domain routing or CIDR was introduced. And of course, in today's networks we see that with very few publicly available IP addresses and by using NAT, the organizations expose only a single or a handful of public IP addresses and provide internet connectivity to thousands of their internal nodes. However, this was one of the prime motivations but it was not the only motivation that led to the emergence of IP version 6. The next one of course was the need for speed because with the emergence of fiber optic communication systems the bit error rate started to drop and it got much better to an order of 10 to the power minus 9 to 10 to the power minus 11 which is the ratio of the number of bits going in error. With such reliable optical communication on the long haul, IP version 6 was thought as an alternative to IP version 4 which implements checksum as an error detection mechanism. And of course we know that the internet of things requires everything to have a publicly visible IP address. These requirements were to be fulfilled so came in IP version 6. IP version 6 with all its different packet format that we shall see comes with some unique attributes and features which make it significantly different from IP version 4. For instance, it has a provision for per flow quality of service. You know that quality of service is normally assigned on the basis of the type of service field available in IP version 4. However, that was on a per packet basis. IP version 6 provides a mechanism which is on the basis of flow label. It's an important field in the IP version 6 header, the source and destination addresses. So with the concatenation of all these three, the flow is established between a certain user and its end point. So this particular flow is given a certain kind of quality of service treatment. The next important feature in IP version 6 is the next header field. By default, the header size in IP version 6 is 40 bytes, but it can always be extended. The need for extension is obvious. Like in IP version 4, the original IP address, the IP header was 20 bytes, but it could be extended up to 40 bytes. Here in IP version 6, the requirements such as appending the routing information such as the loose source routing, strict source routing, root recording and the AAA mechanism, these additional features could always be incorporated in the header by using the next header field. Since there's an understanding that the end devices and the intermediate devices like routers are high end, so as such, there wouldn't be a requirement to fragment the IP version 6 packets. And IP version 6 packets are carrying a lot of data from the sender to the receiver, so fragmenting them would have created lots of packets. So by just doing away with the fragmentation requirement as such, IP version 6 makes the processing of a very large packet very quick because the overall header to payload ratio is very much high as compared to IP version 4. And to maintain and ensure speed at the wire line, the checksum was there in IP version 4 has now been omitted in IP version 6. The IP version 6 header is shown to you here. We just quickly go over it. We see that there are certain fields like version, similar to the previous one, the traffic loss, quite similar to the type of service field, flow label is a new field, payload length, similar to the last one. The next header is what we have already talked about. Hop limit is akin to TTL, the time to live. And the source and destination addresses here have now been extended from being 32-bit to 128-bit. So there is a significant, in fact, very large increase in the overall address space in IP version 6.