Stickfight

Category JAVA DNS Domino
This is a very old bug but affects at least Java 1.4 though 1.6 so pretty much hits all versions of domino, the problem is:

"Once an application has performed network access (i.e. urlconnection, parsing of xml document with external references, etc), the DNS settings get cached so any subsequent operation will use the old settings even if the real settings have changed. To reset everything, you have to restart the server since the default setting JVM setting is to cache forever."

I.E., if any of your Java on domino makes a call to a website or network resource, and that resource changes its IP address, you have restart your JVM and therefore your whole Domino box, most people will restart a server to try and fix an unknown problem anyway so the problem will seem to have fixed its self, but some times its good to know why (i just hit it on my use of reCAPTCHA as provided by Chris Brandlehner)

sources:

http://stackoverflow.com/questions/1835421/java-dns-cache-viewer
http://www.rgagnon.com/javadetails/java-0445.html
http://www.mattryall.net/blog/2005/03/javas-awful-dns-caching