Hi,
      I have a device that I can't add a default gateway but I want a service from this computer from an other network. So I think I have to use NAT. What I did is this:
 
int tunnel2
ip add 10.1.1.2 255.255.255.0
ip nat outside
 
int gi0/1
ip add 10.1.2.1 255.255.255.0
ip nat inside
 
ip nat inside source static tcp 10.1.2.100 6010 10.1.1.2 6010 extendable
 
So, in the client computer from WAN, I use 10.1.1.2:6010 to communicate with 10.1.2.100:6010.
 
In this case, the device 10.1.2.100 suppose to answer to 10.1.2.1 (int gi0/1) and than if no gateway on this device it suppose to work?
 
Let me know if I'm completly wrong. 
 
Thank you