Ubuntu server router as gateway mode to router mode?
 

based on this sample guide link:
http://ubuntulinux.co.in/blog/ubuntu...les-in-ubuntu/

with this code:

it means that "All PC’s on the private office network should set their “gateway” to be the local private network IP address of the Linux gateway computer."

How can we make our ubuntu server router gateway mode to router mode? In order our private networks is visible from other networks or different subnet.

I'm sorry, but it's next to impossible to understand exactly what you're asking here. I could make some guesses, but I'd probably be wrong. Your description of the iptables command doesn't really make sense either.

Perhaps you could try and explain exactly what you want to accomplish? Is the Ubuntu system to be a router between different IP networks? Does the setup involve Internet connectivity? Perhaps you could post a network diagram?