DNS logs
You can configure DNS to write logs, and I recommend that you do so. DNS logs can be an invaluable source of information on what went wrong, when it went wrong, and sometimes even why it went wrong. To set up logging, start the DNS MMC by clicking Start | Programs | Administrative Tools | DNS. Right-click your DNS server, choose Properties, and then go to the Logging tab. You can then select the types of DNS actions you'd like to log. By default, Windows 2000 locates the DNS log in the %systemroot%\system32\dns\dns.log file. If you want to change the path to the DNS log, you can do so in the registry. Open the server's registry and change the value of:HKLM\System\CurrentControlSet\Services\DNS\Parameters\LogFilePath. The DNS log file is limited by default to 4MB. Like the log file location, you can change the size of the DNS log file by making changes in the registry. To do so, you need to add a REG_DWORD entry called . Be careful in the registry
Remember to use caution any time you edit the registry. It's wise to perform a full backup before you change anything in the registry. Check your cache
DNS stores its name resolution information in files called zone files. There are four types of zone files in Windows 2000: Primary, Secondary, Reverse, and Active Directory Integrated (ADI). DNS includes another important file called CACHE.DNS. CACHE.DNS is not really a zone file, but it holds the same kind of information as a zone file. One of the most common problems encountered when working with DNS servers is corruption of the CACHE.DNS file. If your users can resolve everything on the local private network but can't connect to any Web sites on the Internet, this may point to a problem in the CACHE.DNS file. To remedy this situation, first ensure that the DNS Server service is stopped. Then just pop in your Windows 2000 Server CD, find the CACHE.DNS file on the CD, and copy it into the %systemroot%\system32\dns directory on your server, overwriting the other file. Then restart the DNS Server service and check to see if name resolution is working again. Breaking down the problem
After you've eliminated all other potential causes of name resolution failure, you're left with the DNS server itself. A Windows 2000 DNS server is most likely to fail on startup, so the most important thing at this stage is to understand what files and processes are involved in starting or booting a DNS server. The files involved, in order of use, are:

• BOOT: The BOOT file does two things: It tells the DNS server if it's a root server, and also if it's a primary and/or secondary DNS server for any DNS naming zones.
• CACHE.DNS: This file lists so-called root hints relevant to your DNS installation's top-level servers. By default, the file contains the names and IP addresses of all 13 Internet root servers. This is because DNS is most often used for Internet name resolution; but if your network is disconnected from the Internet, your DNS servers act as root servers.
• Zone files: There is one zone file for each zone hosted on a particular DNS server. The zone file contains all machine names and IP addresses relevant to the domain whose information is stored in the zone file.

You can initiate the startup process for a DNS server from three sources: the BOOT file itself, Active Directory, or the registry. By default, a Windows 2000 DNS server stores all startup information in Active Directory or the registry, or a combination of both. Normally this is fine, but you may want to consider changing the way DNS starts by having it start from the ASCII BOOT file in the %systemroot%\system32\dns directory. Starting DNS from the BOOT file simplifies troubleshooting and repair because you can manually edit the BOOT file using any text editor, should you need to. To change the way your DNS server starts, open the DNS MMC, right-click your server's icon, and select Properties. When the Properties window appears, click the Advanced tab. Finally, select Boot From File from the Load Zone Data drop-down list box. You can accomplish the same thing from the registry by finding: HKLM\System\CurrentControlSet\Services\DNS\Parameters. Check to see if it contains a BootMethod entry. If BootMethod doesn't exist, you can create it as a REG_DWORD, setting its value to 1. Values 2 and 3 cause DNS to start from the registry and Active Directory, respectively.