NAT address
 

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As you don't know what the ip is, I assume that you haven't changed it, which means it will have the default ip, which can be found in its manual.

or open a command prompt (Windows - Start -> Run "cmd") and type ipconfig /all
the router IP will probably be listed as 'default gateway'

I know the IP of my router, but is Roter IP and NAT IP the same ??

A router has two IP addresses (that's why it's called a router). One LAN address (192.168.x.y) and one WAN address (see link above). NAT (network address translation) translates between the two. There is no NAT IP address.

Ok, its a new area for me..

Here is the PB:

""4.6.5 Option 8 - NAT Address

If the L-IP is used behind a NAT router the public IP address of the NAT router or firewall must be known. This address can either be entered manually or can be determined automatically. Automatic NAT router discovery allows to operate the L-IP behind a NAT router or firewall, which has a dynamic public IP address, and determines the correct NAT address from the L-IP CS. This is the default setting in firmware version 3.0 and up. ""

Any idea what address it is then ?

That would be looking for the WAN address. The LAN address is very easy for a program to determine automatically. Also "public IP address" translates into WAN. 192.168.x.x are private IP addresses as they are not routable across the internet.