I have tried several times to Port Forward this router,but at the end of the day it never works.By that i mean my port isnt open.
I am trying to port forward for a Minecraft server to play with my friends.
My router's model is ASUS RT-AC51U.
I'm assuming you already went through this, but please confirm you've set it up as described below and tell us the outcome (port range, local IP, local port, protocol)
This 5 minute guide is used to open your ports for the Asus RT-AC51U router. It only takes 4 steps and you're done.
portforward.com
I found that site some years ago when I was struggling to configure DSL modem/router with proprietary firmware loaded by the Mexican ISP. I bought the Network Utilities suite of tools for U.S. $40 and in my case it was money well spent. I would suggest first trying to follow the tutorial above, then if that fails go ahead and purchase the Network Utilities that proved so helpful to me when figuring out the undocumented firmware in my DSL modem/router.