Thanks a lot for your reply.
The link is showing internet connectivity is happening only on one subnet 192.168.1.0/24 but my situation is bit different. I have onky one static IP address from ISP (10.10.172.41/25) and Gateway is 10.10.172.1. I configured these ip addresses in my WAN (wired) connection. My IP 10.10.172.41 is dedicated and I can't use any other IP else authentication will not happen.
Now I want to create separate network for my internal LAN (wifi) and using default ip of Arduino Yun 192.168.240.0/24 with DHCP enabled and connect to internet using NAT or any other method so that all of my outgoing request would happen through ip 10.10.172.41 only.