Although ISA Server 2006 has a great Sharepoint Wizard to configure Sharepoint/MOSS Publishing rule sometimes what was supposed to be simple can became a nightmare. Most of the times ISA gets beat first since it is the device that faces Internet and users from outside are the ones that are complaining about. However if there are so many elements that can cause issue of this nature that simply stick in mind that ISA is the culprit is just not realistic.
Recently a friend of mine from MOSS Team wrote an article that fixed an issue where has all the ingredients to make you think that ISA was causing the issue. The problem started because something call disk-based cache, AKA BLOB (see this article for more info). Here it is the scenario and when you read NLB, think about ISA NLB using Web Farm to publish MOSS with a configuration similar to this one for the Web Farm:
“One probable and common scenario is that on which you have multiples Web Front End (WFEs) and they are reached via Network Load Balancer (NLB). You did not add any host header when you created the web application and yet you can access the web application using both the local server name (eg. MOSS-WFE01) or the DNS entry (eg. http://myportal.contoso.com). However, when you add blob cache functionality to the site (see how to do this here), the cache does not seem to (and actually does not) work.”