‘If you cannot resolve a name, but using the IP address of the host seems to work, you may have a problem with your DNS server. If your DNS server is local, it is easy to check, but if it is remote, you can use a utility called Nslookup.
Nslookup is a utility that was originally included with BIND, and is used to connect and troubleshoot a DNS server.
The command to start the utility is pretty straightforward. You just type nslookup from a DOS prompt or directly in run command line under the start menu. The utility will automatically look for the DNS servers you or your DHCP have specified in the search order on your client PC.
After nslookup finds a server, you are presented with a > prompt. From this prompt you have several options. By entering ? it will bring you a list of all the command line options available.
Some of the most popular commands you will use include set and ls. Nslookup searches for entries in address (A) records. The set type allows you to change the default query to a new record type. For example you can use the set type command to change the record type you want to search for. (e.g. set type=MX looks up mail exchange records, NS nameservers, ALL all entries)
The ls or list of files command is a popular UNIX command for looking up files and directories. Nslookup uses this same command to list all the DNS servers and records.
The ls command may cause load issues on the DNS servers and also list all information available for that domain thus it is most commonly refused.
Nslookup is also useful for querying authoritative DNS server (DNS server that is carrying the info for a particular domain) for checking problem in configuration and also for obtaining information for a domain.
Generally, unlike ISP’s DNS servers, domain registrar’s DNS servers do not respond to directly queries for DNS zones that they are not authoritative for.
If you combine these simple tools with some logical troubleshooting and isolation steps, you can resolve many network problems. Look at the inevitable troubleshooting as another chance to learn more about the powerful communication system called TCP/IP.