Steps on how typing a web address finds its way to the web se rver, via DNS

[Michael Breton]

> -----Original Message-----
> From: dominick at cyberspace.org [mailto:dominick at cyberspace.org] 
> Sent: Wednesday, October 29, 2003 4:27 PM
> To: comp-protocols-dns-bind at isc.org
> Subject: Steps on how typing a web address finds its way to 
> the web server, via DNS
> 
> Hello Gurus:
> 
> I want to know the step-by-step procedure of how a request to 
> a web site gets to the server from the client. Specifically, 
> how does this work? For example, when I type 'abc.xyz.com' in 
> the address bar, what are the steps to its destination? I 
> know there are .com, .org, .gov, .net, etc. root servers. So, 
> when I hit enter, first, is the address looked at from .com, 
> first, then .xyz.com, then finally abc.xyz.com? I'd 
> appreciate a clear explanation from a DNS expert. Thank you.

The client PC asks their local DNS server 1.2.3.4 for an A record for
abc.xyz.com

The local DNS server looks in it's cache to see if it already has the
answer, if so, it answers immediately.

The local DNS server asks for an A record for "abc.xyz.com." using the root
servers for ".".  Instead the root servers reply with the nameservers for
the ".com." TLD.

The local DNS server looks for an A record for "abc.xyz.com." using one of
the nameservers returned from the previous query.  Instead, the nameservers
reply with the nameservers authoritative for the "xyz.com." domain.

The local DNS server looks for an A record for "abc.xyz.com." using one of
the nameservers returned from the previous query.  Generally the nameservers
reply with the A record as requested.

The local DNS server replies back to the client with the A record requested.

The client sends it's request to the webserver.

Of course, if any of the information above is in the local cache, the local
DNS server will use that before querying for it.

There is more information being passed, but that is the basics.

I hope that helps...

Michael Breton
Commtel