It is safe to assume that most internet users have no idea what DNS caching is or how it helps the flow of information on the WWW. That being said, I suppose for the average user, knowledge of DNS caching is not important; however, to anyone involved in the IT field it is an important concept to know.
DNS Caching
While it is probably hard to determine, it is safe to assume that there are probably millions, if not billions of DNS requests going on at any one point in time. If every time a DNS lookup is requested the request has to work itself all the way to the top of the DNS hierarchy, there would obviously be a large bottleneck that occurs within nanoseconds. This would cause the entire internet to effectively shutdown in short order. It would also make the responses incredibly slow.
To avoid this situation, DNS caching is used. This way the information is stored lower in the hierarchy so that DNS requests can be handled and responded to in an orderly and efficient fashion. In contrast to the former situation, when a user makes a DNS request, it may only have to go to their local DNS server (in the office, or even on their computer) to get the correct IP address of the domain they are looking for. Not only does this reduce the probability of a bottleneck, it also allows for much faster browsing - no matter what speed of internet the user has.
IPv6
Theoretically, even with the advent of NAT, IPv4 addresses will run out within the next couple of years. With hundreds of millions of pieces of technology that require an IP address, IPv4 addresses are now becoming very scarce.
While it is not known if the IPv6 convention is the best idea, or easiest to use and implement, the number of possible addresses is, as far as we can fathom, sufficient in terms of addresses.
As St. Sauver points out in his article, IPv6 uses 128-bit addresses, which should allow for address assignment for virtually any conceivable address allocation scenarios. A complicated mathematical equation shows that it is possible to assign "3.7X10**21 addresses per square inch of the earth's surface"(Sauver, 2001, para. 11)!! I could not possibly imagine that ever being necessary.
References
St. Sauver, J (2001). What's IPv6....And Why Is It Gaining Ground? Retrieved January 15, 2009, from http://cc.uoregon.edu/cnews/spring2001/whatsipv6.html
Karrenberg, D. (February 2004). The internet domain name system explained for non-experts. Retrieved January 15, 2009, from http://www.isoc.org/briefings/016/index.shtml
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