Primary DNS server is unreachable

Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries the Win32_NetworkAdapterConfiguration Microsoft Windows® Management Instrumentation (WMI) class to obtain the DNSServerSearchOrder attribute. This attribute is an array of server IP addresses to be used in querying for DNS servers. After retrieving the address of the primary DNS server, the Exchange Server Analyzer opens a TCP socket connection to port 53 on the server. This connection is made by using a custom object processor that returns a specific string if the connection is successful. If the Exchange Server Analyzer does not receive 53 Available as part of the returned string, a warning is displayed.

This warning indicates that the server did not respond to a connection attempt on TCP port 53. By default, DNS servers listen on TCP socket 53 for communications such as name resolution queries.

If the primary DNS server is unreachable and you are running Exchange 2000 Server, mail delivery will be slow. A supported hotfix is available from Microsoft to correct the problem of message delivery to external recipients being slower than expected when the primary DNS server is not available. Contact Microsoft Product Support Services to obtain this hotfix.

Additionally, you will want to troubleshoot why the primary DNS server is not available, or change the DNS settings on the Exchange server to use a different DNS server for name resolution.

To correct this warning

Make sure that the DNS server has been started, and that it is connected to the network.
Use the PING command to determine whether the DNS server is reachable.

For more information about slow mail delivery when the primary DNS server is not available, as well as how to obtain a hotfix for this issue, see the Microsoft Knowledge Base article 829722, "Mail delivery is slow in Exchange 2000 when the primary DNS server is not available" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=829722).

For more information about DNS and Exchange Server, see the following Knowledge Base articles and WebCast:

322856, "How to configure DNS for use with Exchange Server" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=322856)
263237, "XCON: Windows 2000 and Exchange 2000 SMTP Use TCP DNS Queries" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=263237)
324759, "Support WebCast: Microsoft Exchange 2000 Server: DNS Troubleshooting in Transports" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=324759)