I've set up a ubuntu server (14.04) to act as a router between our local workplace network, internet and corporate network.
The server has three network interfaces:
My ubuntu server has joined the active directory (likewise-open), this is needed to have access to the intranet, SAP and so on. It receives an IP address from the corporate dhcp server.
This is just connected to a "clean" internet line.
Running DHCP server for local network.
I have configured iptables according to this (with some small changes): https://help.ubuntu.com/community/Router/Firewall
It is routing traffic from clients to the internet, so everything seems to be in order.
What is left to do is to make iptables send traffic from clients that has a certain destination ip to the eth0 (corporate), and make it look like the traffic is coming from my server. And allow incoming traffic from those same ip's.
So if anyone could point me in the right direction I would be truly grateful.