resource.down() problem

Dear all,

We are now using CE 7.3 to develop web dynpro java applications and everything runs ok in our internal network. But recently we publish a eternal url for users and we use a DNS to parse the url to point to the internal address, and we encounter a problem, as follow:

we use resource.download() to export excel, but it doesn't work after we use the eternal url. So we check our code first,

version1:

IWDResource resource = WDResourceFactory.createResource(inputStream, "XXX.xls", WDWebResourceType.XLS, false);

resource.download() ;

version2:

IWDResource resource = WDResourceFactory.createResource(inputStream, "XXX.xls", WDWebResourceType.XLS, true);

resource.download() ;

version3:

IWDResource resource = WDResourceFactory.createCachedResource(inputStream, "XXX.xls", WDWebResourceType.XLS, false);

resource.download() ;