I have clients that will be connecting to a server (ServerA) through a switch. ServerA connects to the switch through eth0 and i use another ethernet card - eth1 to connect to the Internet through an ADSL router. The clients can access the internet with no problem, i have set up IP forwarding and IP masquerading on ServerA. The problem is that i have another server (ServerB) with an external IP address which is where i want all the traffic from the clients to pass through before going out to the Internet. So i want any clients internet access to go out through the ADSL router into the internet and then through ServerB before going to the actual Internet site. ServerB is where the billing and statistics of the clients will be recorded, so I need to pass the clients requests through ServerB. I cannot modify the ADSL router configuration and I dont want to use VPN. Is there some way to achieve this by modifying ServerA or ServerB? I am using Linux Red Hat 9 on both servers with Apache version 2 and also running a DHCP server and a DNS server.

Instead of having ServerA connected to the ADSL router, connect it to ServerB and let ServerB connects to the ADSL router. Configure IP forwarding and masquerading in Server B. In effect, ServerA will just be a connecting bridge between the clients and ServerB. Inconclusion, better let ServerB connects to the switch and remove the involvement of ServerA in this scenario, yes?

Thanks for the reply cyberarachnid. ServerB has to remain external because it will be located in another country to serverA, that is why it has an external IP. I want to direct the traffic from serverA over the internet to serverB. Very much like VPN but i was hoping there was another way to do it.

Not sure if it is exactly what you are looking for but a transparent proxy may help. Failing that can you not store the relavent information on ServerA, share it as something like an NFA share which can be mounted and read by ServerB's accounting software? Thinking about it a transparent proxy may work by forwarding all web traffic to an external server just as you would do with a firewall and an internal proxy server.... http://www.tldp.org/HOWTO/TransparentProxy.html