Hi Prashant,
If the 2 sites have the same addressing scheme, ie 192.168.1.0/24 is the same LAN on both sites, then you need to carry out double NAT.
ie NAT your own LAN behind another range, ie 10.1.1.0/24 and the 2nd site LAN to be Natted behind another unique network, ie 172.16.1.0/24.
You have to NAT both sides to make sure that basic routing will work, ie if you dont nat the 2nd site IP range, you will be sending traffic to their LAN on 192.168.1.0/24 as above, which will get to your router, it will see that 192.168.1.0 is local, so sends back into your net.
You can refer sk101460 for more understanding. Hope this will be helpful.
