Exchange doesn't work if Exchange Server is not set as primary DNS

So I have a client running a Server 2008/Exchange 2009 box, which is set as the DNS and domain controller.  He is using a local T1 company, and their router is working as DHCP.  During the initial setup, we realized that if the server was not set as the primary DNS on a local computer, then exchange was unable to connect.  So I said no big deal, and set the DNS server, and all was well.  Now the customer is having issues with internet speeds and the T1 company is blaiming it on our windows server.  So in order to prove that it is their issue and not ours, we need to be able to set their router as DNS without losing exchange functionality.  Any help would be appreciated!
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How many machines are we talking about? You can use their external dns and configure hosts file manually during the interim.

Alternatively, you can test bandwidth speeds and congestion using various network tools and supply the provider with stats.
qbarat2Author Commented:
I tried a lmhost entry but I am unsure if I set it right.  Lets say the exchange server name is and the local IP is, what would the proper entry be?

Open the following file... C:\WINDOWS\system32\drivers\etc\hosts

and add this line to the bottom below "       localhost"

Once you open the file you will also find examples which are commented out.

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In AD, the domain controllers MUST be using themselves for DNS only. No external DNS. All clients must also use AD DNS servers for DNS only. Anything else will cause a problem because of the DNS issues.

This sound like standard ISP support practise - basically find something else to blame the problems on. DNS would have nothing at all to do with the speed of the internet connection. All DNS does is lookup the IP address. As long as name resolution works (ie the site can be accessed) then the server is not the cause of the problem.

The ISP has to be told to stop trying to pass the buck. Lie to them if you want, the ISP is almost certainly lying to you.

qbarat2Author Commented:
I know this is an ISP issue, but we've been going back and forth for weeks now so I want to be able to prove to them and the client without a doubt it is their problem, forcing them to take the necessary action.  These solutions are very helpful, I will impleent them and let you know the results.  Thanks!

Mestha is correct regarding the dns configuration but I was hoping to get a couple clients to test this in order to accomplish two things still be able to connect to exchange and use external dns servers to browse the internet just to satisfy the ISP's request.

If you prefer not to go this route. Then just plug in a laptop on the network using the external dns servers and sit next to another machine using internal dns servers. Surf the web on both and compare the speed and response times. Then call the ISP and do what you have to in order to move forward.

Once you have them on the phone I would ask them if the circuit is being overutilized. If not, how much bandwidth is currently in use. Do they offer any bandwidth management tools and etc.
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