3

You should disable caching of the redirection page. There are exist two options:
1) on the web server

Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Pragma: no-cache

2) add the ? sign to the url of the ntf_server option, it will differ from time to time

ntf_server=192.168.0.18/ntf?

about ntf_server option