Hi
@chinninitin , I had a decent chat with BSNL officials of my area and at least here they are not blocking ports from being opened or forwarded.
Regarding your queries:
1) I know our
routers have NAT 1-4 but back when I was doing my hit and trial experiment with port forwarding every where on the internet i could only find NAT 1-3 with the following categories:
NAT 1(Great but largely open and less secure)
NAT 2(best mix of security and being open to requests from outside the network)
NAT 3(very restrictive and secure as well but may create problems for requests coming from outside the network)
MINE IS SET TO NAT 2
2) DMZ doesn't have to be enabled for enabling port forwarding. Large businesses may use DMZ to keep their servers hosting their public website(which is accessible to the whole world) separate from their internal servers (only accessible to the employees etc. of the company) on a single network.
MINE IS SET TO DISABLED
3) This is the part which is most ambiguous on the internet because the particular nametags ("Server IP Addr" and "Internet IP Addr") used by these cheap routers are not explained easily on the internet, so your understanding pretty much matches mine on this one. So basically this setting is required so that :
3.1) External devices send packets to the external IP address (Internet IP Addr) and port (External start port and External end port)
3.2)The NAT router maps those packets and re-transmits those packets on the Internal network to the internal IP address (Server IP Addr) and the Internal Port (SPORT).
One important thing is that you need to assign your device the one that needs to communicate with the outside devices to have a static internal IP address (e.g : 192.168.1.10) which you will then fill up in the Server IP Addr field and leave the Internet IP Addr field empty if you have dynamic Ip and in case you have a static IP assigned from BSNL then fill that one instead and the respective ports which need to be opened as per the internal and external side of the network.
4) UPnP, if you enable it then you don't have to open or forward any ports as it will automate that process for you but it will do it for any kind of incoming request coming into your network from outside on any port and hence it is less secure, so i personally recommend to port forward only the required ports.
MINE IS DISABLED
If you have any other doubts do let me know, I'd love to help you with that document.
Again I'm no expert in this it's just what I learned from my hit and trial attempts, but I'll try to help as best as I can.