DNS nslookup Error Message connection timed out; no server could be reached

While I configure DNS In the Linux Red hat Version.
I configured ever thing perfectly. But after I configure, While I try
#nslookup rhel5.com (or) dig rhel5.com
I got the following error message.
;; connection timed out; no server could be reached
I try lot of forum. But I didn’t get the any proper Solution.

Then I analysis with my self.
Error message “connection timed out; no server could be reached”.
From these error message I got  idea. these is the problem occur in the Network or security.So I configure network perfectly.Then I disable the iptables and selinux.Then still I got the same error message.

Then I install the new Linux redhat in my vmware.
while I installing I disable the iptables and selinux as disable mode.
Then I configure DNS Finally the problem has been resolved.
Earlier while I install the red hat Linux . I enable the firewall iptabels and selinux.After configure DNS even though I disable it is connect to server.These is problem. Finally the problem has been resolved.
DNS configured successfully.
;; connection timed out; no server could be reached .dns red hat vmware nslookup dig nslookup