Primer on DNS....

I received several hundred e-mails all asking the same basic questions "why can't I see my web page at home when my friends can see it or I can see it from work" etc.

Let me take a minute to explain how DNS works and how it interrupts your use when the server has to move locations.

On the Internet there is a sort of sub-network whose only job is to help your computer find the computer you are looking for. This is DNS or Domain Name Service to be exact. Every computer in the world has a unique number assigned to it called the IP (Internet Protocol) number. This number is assigned by the provider of your Internet connection. Most computers also have a name called a "hostname", WWW is a hostname, QSL.NET is a Domain name. Hostnames and Domain names are for humans, computers want IP numbers so there is a system that translates names to numbers and numbers to names.

Internic (commercial company now, used to be a government funded entity) owns the "ROOT" DNS servers. When you register a domain name you specify what server IP you will use to be the authority for your domain to IP translation. The ROOT servers don't know where your domain is they only know who does know....Your DNS server.

Your DNS server contains a database that maps all your hostnames to IP addresses and vice versa. Every computer that has ever looked at WWW.QSL.NET came to the DNS server for QSL to find the information on how to communicate with the server(s).

OK so now to the problem at hand. Why does WWW.QSL.NET suddenly disappear if it changes networks (and gets a new IP number). Every request to the QSL.NET DNS server is answered and the requesting system is told how long the data will be valid ( usually 4-7 days) this is called the TTL ( Total Time to Live). The server that requested the data stores it for that long and gives the same answer until it's "Cache" expires and it asks again for the info. Any answers it gives after the WWW.QSL.NET server changed IP's is wrong and results in the "404 error" page not found. This is not an error in your DNS server, it just means it's doing as it was instructed but the game changed with out it knowing or being able to find out.

This caching of DNS is why the server goes away when moved. To help correct this problem before scheduled moves I lower the TTL to 1 hour for about a week....The DNS servers get pounded hard because of this but a move only means you have to wait 1 hour at most to have the correct information again. When you do an emergency move as I did last week and the TTL was at 4 days it could take from 1 minute to 4 days to get the correct information depending on where the timer on your DNS cache was at that moment. Hence people in different domains get the updated info at different times.

So this is more than you wanted to know about this entertaining subject....would you believe books have been written on this, better than Chloroform for sleeping

73, Al