Just a little 'hack' if you like me have the Korean SK Telecom Router H633G which is from Huawei, and you want to port forward one of the blocked ports like port 80 or 443. It's just a check in JavaScript so it's easy to bypass:

Open the NAT page but without the stupid frame, so http://192.168.55.1/nat_functions.html then in Chrome right click -> Inspect -> Console. And there write: function checkBlcokPort() { return true; } and press Enter. After that the function is overwritten and you can safe it.

(The typo is in the HTML source code of the router, not made by me.)

Thanks for the initial idea to this video: https://www.youtube.com/watch?v=BvmnbT3yV6Y