Why was this question closed: https://superuser.com/questions/223366/can-ping-ip-address-and-nslookup-hostname-but-cannot-ping-hostname-closed ? Please reopen it since it hasn't been fixed yet.
Your question was not closed. It was migrated to another StackExchange site called ServerFault. Here's the new link to your question:
For future reference, questions regarding Server operating systems and enterprise-level networking are not appropriate for the SuperUser environment. Please post such questions to ServerFault instead. SuperUser is intended for questions about Workstation operating systems and Small Office/Home Office (SOHO) networks.
If you look at the stated reason for close you will see that it was migrated over to serverfault.