@VivekDragon 

Hi,

There could be several things that need to be done, but first we need to find out if your Internet Service Provider is assigning a public IPv4 address to your Internet connection.

Please log into your C5's configuration interface (via http://tplinkwifi.net or http://192.168.0.1) and post a screenshot of the page you see in below picture. (you can black out the rightmost numbers if you wish)

If the cable that is plugged into the WAN port of the C5 goes to another device that is accessible to you (like a modem), then please let us know the make, model and version of that device as well.

@VivekDragon 
Hi,

       Thanks for the quick response. I am attaching the details you have requested. Hope those are enough. let me know if any other details needed.

Router is connected to a modem.
Make: Opti-Link
Model:OP-XONT
Version:OP=XONT 71000

@VivekDragon 

According to this page https://en.wikipedia.org/wiki/Reserved_IP_addresses your Internet address falls within the IP range that is used by Internet Service Providers for carrier-grade NAT (CGNAT).

In simple words this means your ISP has placed another NAT router between you and the actual Internet, which makes NAT Type A for your Nintendo impossible.

You can confirm this by going to an IP check website like https://www.ipchicken.com and you should find that your IP address as seen from the Internet is different to the Internet IP address shown in you router (100.122.x.x).

What you could do now is to contact your Internet Service Provider and ask if they are able to assign a "public" IPv4 address to your Internet connection. (if that was successful then the IP address shown by https://www.ipchicken.com and the IP address shown on the "Status -> Internet" page of your C5 router should be identical)