my all workstations and servers shows internet connectivity. 100mbps

i can receive all emails from outside world and send email to outside world in my organization.

but i cannot open any websites like yahoo, hotmail OR any other site.

i checked my router, it works fine when connected directly to my laptop , i can open internet.

but as soon as i connect my router to my watch guard firewall my internet is not working

All my servers are connected to watchguard firewall through switch box.

my router- firewall-switch box (network ports)

i got it verified from watchguard technical , there is nothing wring in firewall policies or physical device itself.

But when i used google dns and comcast dns on my workstation then my internet works fine bypassing my internal dns server address  so the problem has come to my dns server internally in my office.

what should i check in my dns server  i have dns, dhcp, exchange, active directory on one server windows server 2008 sp2. i have exchange 2010 sp2 installed

my internal dns is not working correctly.

what should i do to correct the problem, i rebooted my exchange server which is having dns but it is not working.
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Is there any useful info in the Event Logs? You might also try perfmon and dcdiag. From a command prompt dcdiag /dnsall (to run ALL dns tests) or dcdiag  /h will show you a list of diagnostics and under DNS you will see the various switches it allows.
Adam BrownSr Solutions ArchitectCommented:
You probably need to set up a DNS forwarder or make sure the existing DNS forwarders are valid. Open DNS, right click the server name, click properties, click the forwarders tab. Make sure all the entries in there are valid. If you like, you can just set it so it users Google dns. If you've recently changed ISPs, the Forwarders you have may be invalid.

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