From: e8mhpsznamq001@sneakemail.com To: list@maradns.org Subject: Common misconceptions about DNS There is a common misconception about DNS floating around that it is up to the DNS servers serving a given domain, such as example.com, to tell all the other DNS servers in the world when a change happenes to one of the host names in the domain. The idea is that such a change is somehow propagated through the internet is very common. It is also incorrect. DNS was designed in the bad old days of the internet. The days when the backone of the internet was a 56k link. The days when 5 minute timeouts for telnets were needed; a timeout any shorter would prematurely disconnt someone. As a result, it uses caching to store data. However, an ISP's DNS servers do not cache the information about, say, www.maradns.org, until someone asks the ISP's DNS server about maradns.org. At which point, the ISP server will find the DNS server for maradns.org, find out the IP for maradns.org, and also be told how long to cache that data. Clear as mud? Let me word that differently. Some enlightened person on the internet wants to find out more about MaraDNS. So, they whip out Mozilla and decide to go to maradns.org to find out more about this wonderful (newly nearly bug-free [TM]) piece of software. Now, before they can go to maradns.org, they need to find out where maradns.org is on the net. Which requires a rather ugly process called DNS. A process so ugly that most people's home computers don't even bother with this process. Instead, they ask their friendly local ISP's DNS servers where they could find maradns.org on this here internet thingy. So, the home computer asks the ISP's DNS server "Hey, where the heck is MaraDNS org". At this point, the first thing the ISP's DNS server does is look in their cache. "Hmmm, did someone recently ask about maradns.org?" asks the ISP's DNS server. Well, how about that, no one recently asked about MaraDNS. "Oh dear; I have to find where it is on the internet now. Oh, God, please not let this be a host name with out-of-bailiwick name servers." So, to make a long sorid story short, eventually the ISP's DNS server hooks up with the authoritative DNS servers for maradns.org. You know, getting the answer straight form the horses mouth and all that. So, the ISP's DNS server saunters down to the maradns.org name server and asks where it could find maradns.org. The process goes like this: ISP DNS server: Hey, where can I find maradns.org? maradns.org DNS server: It's at 66.33.48.187; remember that for one day. This means now that, for the next 24 hours the ISP's DNS server will reemember that maradns.org can be found at 66.33.48.187. This way, the ISP's DNS server doesn't need to bug the maradns.org DNS server about where maradns.org can be found. So, what happens if maradns.org has a sudden change of address. Well, while maradns.org's DNS server will give everyone the correct new address, there will be a lot of DNS servers out there which will remember the old address for maradns.org for 24 hours. Because of this, people will be knocking on the wrong door until the ISP's DNS server realizes its postit note about where maradns.org can be found (so that Mr. ISP DNS server doesn't have to go through the sordid process of bugging Ms. maradns.org DNS server again) is out of date; forcing Mr. ISP DNS server to get his lazy butt up out of his desk, find Ms. MaraDNS, and ask her about the whereabouts of maradns.org again. Now, notice something about this entire process. Ms. MaraDNS did not have to do anything but answer Mr. ISP DNS server. Ms. MaraDNS did not have to play the gossip game, where she had to tell all her friends where maradns.org can be found, so that those friends can tell their friends, and so on. Why waste her time being a gossip when all she has to do is sit around and answer questions that various ISP's and other recursive DNS servers ask her? There. Now hopefully I have purged the idea about DNS records somehow propagated from everyone's head. That just ain't how it works. - Sam