DNSCheck

DNSCheck was written to combat a bug in the Windows build of BIND 9. Under load, it appears that BIND 9 simply stops answering queries on either or both TCP and/or UDP ports, although the service continues to run, so service recovery does not solve the problem.

Hollsco Group tried using other DNS monitoring applications, however most of them monitored the UDP port only. When the BIND's TCP port would hang, the other applications would not detect it. Because the TCP port is usually used for zone transfers, this is a critical problem on a primary or secondary DNS.

Hollsco Group decided to write their own monitor. This monitor does a simple lookup against both the TCP and UDP ports at a preset interval. If it receives no response, it initiates a reset sequence that stops and restarts the DNS server.

Technically this application will work on any Windows-based DNS server, although it was written specifically to combat my BIND 9 problems.