A customer was having trouble with this feature of DNS lookup on incoming requests. In order to have a clear understanding of why the DNS lookup was failing.
Diagnosing the problem
There is a configuration option in the NAB that causes the web server to do a reverse DNS lookup on incoming requests. See Internet Protocols -> HTTP -> DNS Lookup.
There is a need to provide custom debug to resolve the issue
Resolving the problem
To assist in troubleshooting the issue a new notes.ini is available.
HTTPDNSDebug=1