Creating a virtual linux router

Hi,

I have an intranet Linux server with 2 NICs, one is the Internet NIC and the other the intranet NIC.

I'm thinking of creating a Linux VM that will be used a router, so, the Linux client will have to use the Internet NIC and then have a intranet IP too.

How can I use the Internet NIC only inside the Linux Client and not in the Linux Host?

Many thanks!

Oliver