The design of IPv6 represented a relatively conservative evolutionary step of the Internet protocol. Mostly, it's just IPv4 with significantly larger address fields. Mostly, but not completely, as there were some changes. IPv6 changed the boot process to use auto-configuration and multicast to perform functions that were performed by ARP and DHCP in IPv4. IPv6 added a 20-bit Flow Identifier to the packet header. IPv6 replaced IP header options with an optional chain of extension headers. IPv6 also changed the behaviour of packet fragmentation. Which is what we will look at here.
Geoff Huston is the Chief Scientist at APNIC, where he undertakes research on topics associated with Internet infrastructure, IP technologies, and address distribution policies. From 1995 to 2005, Geoff was the Chief Internet Scientist at Telstra, where he provided a leading role in the construction and further development of Telstra's Internet service offerings, both in Australia and as part of Telstra's global operations. Prior to Telstra, Mr Huston worked for the Australian National University, where he led the initial construction of the Internet in Australia in the late 1980s as the Technical Manager of the Australian Academic and Research Network. He has authored a number of books dealing with IP technology, as well as numerous papers and columns. He was a member of the Internet Architecture Board from 1999 until 2005 and served as its Executive Director from 2001 to 2005. He is an active member of the Internet Engineering Task Force, where he currently chairs two Working Groups. He served on the Board of Trustees of the Internet Society from 1992 until 2001 and served a term as Chair of the Board in 1999. He has served on the Board of the Public Internet Registry and also on the Executive Council of APNIC. He chaired the Internet Engineering and Planning Group from 1992 until 2005.
Pages created by Geoff Huston
We tend to make a number of assumptions about the Internet, and sometimes these assumptions don’t always stand up to critical analysis. We were perhaps ‘trained’ by the claims of the telephone service to believe that these communications networks supported a model of universal connectivity. Any telephone handset could establish a call with any other telephone handset was the underlying model of a ubiquitous telephone service, and we’ve carried that assumption into our perception of the Internet. On the Internet anyone can communicate with anyone else – right?
One of the more difficult design exercises in packet-switched network architectures is that of the design of packet fragmentation. In this article, I’d like to examine IP packet fragmentation in detail and look at the design choices made by IP version 4, and then compare that with the design choices made by IP version 6.
Every so often I hear the claim that some service or other does not support IPv6 not because of some technical issue, or some cost or business issue, but simply because the service operator is of the view that IPv6 offers an inferior level service as compared to IPv4, and by offering the service over IPv6 they would be exposing their clients to an inferior level of performance of the service. But is this really the case? Is IPv6 an inferior cousin of IPv4 in terms of service performance?
Most of the time, mostly everywhere, most of the Internet appears to work just fine. Indeed, it seems to work just fine enough to the point that that when it goes wrong in a significant way then it seems to be fodder for headlines in the industry press.