The answer is going to make a difference in how you will have to troubleshoot the problem.
For example, if local name resolution works but Internet name resolution does not, the problem may lie with one of your ISP's DNS servers.
Even though many DNS servers use root hints for Internet name resolution, some use forwarders to link to an ISP's DNS server.
And if the ISP's DNS server goes down, Internet name resolution will cease to function as the entries in the resolver cache expire.
The problem was that a virus had integrated itself into the TCP/IP stack and was intercepting all name resolution requests.
Even though this initially appeared to be a DNS problem, the virus was ultimately to blame.After all, if the problem ends up being something as simple as a NIC failure, you can save yourself a lot of time by checking for the problem up front.The easiest way to verify connectivity is to log on to the DNS server and try to ping a few machines.If name resolutions are failing on your local network, try pinging some of the servers on your network. This will confirm that connectivity to the server is working.Next, try pinging by computer name and by the server's fully qualified domain name.Second, if name resolution isn't working, it allows you to confirm which DNS server is being used.Keep in mind that NSLOOKUP will list only the DNS server it initially connects to.If the name resolution request is forwarded to other DNS servers, those servers are not listed. If your primary DNS server is having problems, try using an alternate.If name resolution begins working after you switch DNS servers, you have confirmed that the problem is indeed related to the DNS server and not to some external factor.The result is intermittent connectivity problems to the load-balanced resource.If you determine that local name resolution requests are working but Internet requests are failing, check to see whether your DNS server uses forwarders.