In the beginning, every machine on the evolving internet had its own IP-address. With more and more machines getting connected to the internet,
numbers were beginning to get scarce. A lot of the new machines are connected by using a single gateway to the internet, and the obvious solution was to make the gateway talk to the internet, and to forward the replies to the machines behind the gateway.
So, you are behind a firewall, that does adress translation for you. NAT works very well for you: For example, you connect to Kuro5hin on port 80, Kuro5hin sends the information back to you.
What you cannot do however, is set up your own webserver like Kuroshin, because clients outside would try to connect to your gateway at port 80, which would refuse the connection.
Even if it is possible to configure the gateway to forward the connections to your computer on the local network, this means nobody else on your local network will be able to run a webserver on the standard port 80, because all connections get forwarded to you.
While this may seem to be a small problem, it is a big break with the tradition that started the internet: everyone is suddenly able to run their own www, mud, irc, xpilot, game or news server, the source for which they had downloaded from the internet. The toying with these servers turned many into competent sysadmins and the availability of the source turned many into programmers - many of these people never would have ended in this business, if it was not for these "toys".
The effect of not allowing people to run servers is that the internet is falling prey to businesses, which compete with other businesses on the always same market, for example instant messaging. This would be ok, if not for the problem that the human resources, the hackers, are getting rare, because one magnet, the running of servers, is gone. How else can you explain that internet businesses go bankrupt, while even before commercialisation, equally complex servers and services where available at low cost ?
It is really saddening to me to see this. The tilting of the balance of the internet towards a ratio of a few servers and a lot of clients has become so bad that nowadays, the mere implementation of a peer-to-peer network is a marketing plus, and any application of a peer-to-peer network to a server application is considered patentable !
Folks, the entire internet was supposed to be peer-to-peer !
There are two things you can do: Ask your internet service provider for your own stable internet address, and promote amended internet protocols like IPv6 !
Someone said I was wrong, considering the technical consequences of NAT. I look forward to your comments.
RFC1918 on NAT