I have an old 2003 server (S1) that has been my acting webserver. I have just added a second 2003 server (S2) to use as an ad server. I am trying to set it up so that when I navigate to ads.mydomain.com, it will get forwarded over to S2.
I have gone into the DNS console on S1 and added an A record that points to the external IP address of S2. When I remote onto S1 (whose DNS points to itself) and navigate to ads.mydomain.com, it forwards the request properly to S2 and the ad server site comes up. When I try this from any other workstation, it will not forward the request correctly. It just takes me mydomain.com instead. I have found that this is the behavior that happens when you put in any random string that is not a valid sub domain. The machine does not know what to do with an invalid sub domain and just returns the main domain site.
Does anyone have any idea why it is working if I try it on a machine that points its DNS to S1, but it does not work when using my ISP's DNS servers?