If a query fails because you get the response Non-existent domain from Nslookup or the response Unknown host from Ping, the DNS server did not find the name or IP address that you are looking up. Use the following process, shown in Figure 6.36, to help troubleshoot the problem:
- Check that the client and server computers have a valid IP configuration.
To check IP configuration, type ipconfig /all at the command prompt. In the command-line output, verify the IP address, subnet mask, and default gateway. - Check that the server is working properly. For more information about verifying that the server is working properly, see "Checking the DNS Server for Problems" later in this chapter.
- Check whether the DNS server is authoritative for the name that is being looked up.
If the DNS server is authoritative for the name that is being looked up, you probably have a problem with authoritative data. For more information about checking for problems with authoritative data, see "Checking for Problems with Authoritative Data" later in this chapter.
– Or –
If the DNS server is not authoritative for the name that is being looked up, proceed to the next step. - Query for the name by using Nslookup. At the command prompt, type the following:
Nslookup < query address > < IP address of server >
where IP address of server is the IP address of the server that you queried originally, and query address is the name or IP address you are attempting to resolve. If you get the message "Server failed" or "Request to server timed out," you probably have a problem involving a broken delegation. For more information about problems with broken delegations, see "Checking for Recursion Problems" later in this chapter.
– Or –
If you get an incorrect answer or the message "Non-existent domain," proceed to the next step. - Flush the resolver cache. At the command prompt, type the following:
Nslookup < query address > < IP address of server >
where IP address of server is the IP address of the server that you queried originally, and query address is the name or IP address you are attempting to resolve. If the answer is correct, the problem was a stale cache entry, and your problem is solved.
– Or –
If the answer is still not correct, you probably have a problem with authoritative data. For more information about problems with authoritative data, see "Checking for Problems with Authoritative Data" later in this chapter.
