Seems my network is behind a CGNAT so my WAN IP shows 100* IP and it is different from my public IP when searched over internet and based on the recent exploration seems port forwarding cannot be done for such network? 

  @pallab 

Well, in theory it could be done if your Internet Service Provider was forwarding the ports in question through their NAT to the 100.* IP address they assign to you.

However, I doubt any ISP that is supplying Internet to more than a handful of customers would do that for you, because if another of their customers asked for that same port(s) to be forwarded they would be in big trouble.

Anyway, since your connection type is PPPoE you are probably connected via a DSL or fiber line. ISPs providing broadband Internet via DSL or fiber are usually able to assign real public (dynamic) IPv4 addresses to their customers upon request, either for an additional fee or, if you are lucky, even at no additional cost.
So you could consider contacting your ISP and ask them about it.

There aren't any other simple solutions to this sort of problem.