In the glassfish-web.xml you have the doctype description file linked, like http://glassfish.org/dtds/glassfish-web-app_3_0-1.dtd.
This is downloaded and parsed by glassfish, when our application is deployed. glassfish.org is not available anymore so we changed to http://glassfish.java.net, but even that is not available anymore. Does anybody know, where to find the dtd's?
Maybe we could embed the dtd's as a permanent solution?
Your question is a little bit confusing because these files are actually NOT downloaded from the internet, this would mean that nobody could deploy anything without a connection to the internet.
The files are located in <YOUR_GLASSFISH_FOLDER>/glassfish/lib/dtds/
If you get an error message which says it can't locate the DTD to validate, you may have a formatting error in your XML file. Have a look at this question for more details.