DNS Servers
08.09.06 - 03:00pm
In my previous article I discussed some of the basics of the Internet such as the various protocols and governing associations. Now I’m going to really dig into the Internet and discuss some of the more mechanical workings such as DNS servers, the actual Backbone, and URLs.
When you type in www.gomeler.com into your web browser, lots of things happen to this name before your computer can actually understand it. Servers, computers, and routers all have numerical addresses that describe where they sit in the various networks. Special servers called DNS servers translate the letters www.gomeler.com into the address 207.210.111.10. Now how does this whole system work?
DNS or Domain Name System works in a similar fashion to a binary search tree. You have at the very top of the tree a group of 13 primary root servers that perform all redirects for DNS searches. These root servers will direct computers to the proper top-level domain (TLD) server which serve the .com, .net, .org and other endings to a name. Once you have been directed to a TLD server you are then directed to the next portion of the name such as the gomeler portion of www.gomeler.com. Once you have established the location of this name, your computer queries gomeler.com for the www. portion which makes a connection with the http server at 207.210.111.10. See how simple that was, now imagine doing this a couple hundred billion times a day.
Caching
It would be impossible for the root DNS servers to handle the volume of traffic that traverses the Internet so they rely on caching. Caching is the process of storing data locally on your hard drive so that when you would normally have to download this data you can quickly load it from your hard drive. This not only cuts down on bandwidth but it does a tremendous job in speeding up your Internet connection. DNS caching operates in a similar fashion to data caching. When you enter www.gomeler.com into your browser normally your computer would go on this journey to find the proper IP but what if you have already visited this website lately? Chances are your computer has stored the IP address for www.gomeler.com in its cache and the page will immediately begin to load. These cached IP values have pre-determined expiration dates that dictate when their values need to be refreshed. These expiration dates keep users from being directed to a website that no longer exists if the website is physically moved to another server. Between caching and the distributed DNS network, IP translation queries are responsible for a small portion of website load times.
The Network
In the previous article I briefly touched base with the structure of the Internet. The Internet is a very unorganized spider web of connections between ISPs(Internet Service Providers), universities, government organizations, and large companies. All these connections form a huge web that is naturally very resilient in its unorganized structure. At the center of all these connections is a small network of high bandwidth connections referenced as the trunk of the Internet. These connections are the pipes that feed entire continents and provide major highways for information to travel.
Because the Internet is an intertwined web of connections, it is possible for multiple networks to fail and not bring the Internet down. Just because your browser uses the same route to communicate with this server doesn’t mean it is the only route, it just happens to be the fastest route at that particular time. For example the connection between Atlanta and Houston could be severed somewhere and I’d still be able to view websites hosted out of Houston because of the connection coming in from Chicago. To give you a general idea of what the Internet is like take a look at the picture below. This is a 3D mapping of the Internet that was created by the Opte Project.
Rumors of the Internet
Over the course of a few years a few rumors have popped up especially in regards to web hosting. After reading what I have written perhaps some of them will resolve themselves but the one rumor that refuses to die is the rumor about DNS propagation. Website names don’t take forever to become useful due to a propagation delay, they take forever due to the caching used on webservers. I personally had to deal with this when I switched webhosts from Media Temple to A Small Orange, for about 36 hours the name www.gomeler.com pointed to a website that no longer existed. This was due to the fact that all the subsidiary DNS servers were still announcing my old IP address as the proper address when in fact that was incorrect. Once the cached IP addresses expired and the servers renewed the DNS listings, my webpage popped up. There is no way easy way to get around this system as it is an inherent flaw in the DNS design.
That covers the general structure of the Internet, central DNS servers, a hierarchy of DNS subservers, a trunk of large connections and a web of interconnections. Next up will be webhosting and how one computer can tell your computer what to display. To help illustrate my Atlanta to Chicago point above, here is an image of the UUNET Internet Backbone which is one of many backbones servicing North America.
Very nice article.
Nice article, and I’ll tell my buddy Barrett you used his Opte image. He always likes to hear about clueful people checkking it out. Opte is about to unleash some more killer stuff, but I’ll let him tell you.
As for DNS, there are definitely ways to make DNS cutovers way less painful and I’m happy to talk with you about ‘em if you want.
Take care,
David Ulevitch
I know I’m preaching to the choir here, but one way to clear the dns cache is to go to your command line and type: ipconfig/flushdns. Again, I’m sure you know that.
Ben, actually no I didn\’t know that but I do now. In researching all the stuff for these last couple of articles I\’ve really been filling my head with good wholesome knowledge while answering a lot of questions I had. Thanks for the tip.
David, hope he doesn\’t mind me using the images, they do a very good job of expressing how large the Internet is and exactly how unorganized it is. Wonderful project and I would love to see larger images as it is fun just zooming in and getting lost amongst all the routes.