set up routing over two network interfaces

Question

I'm often on my corporate network but also need to be on another network simultaneously. At the moment I have to manually switch back and forth between the two. I'm using ubuntu 10.04. I've come across an excellent document that explains how to do this: "Linux Advanced Routing & Traffic Control HOWTO" by Bart Hubert. He mentions:

make sure that your kernel is compiled with the "IP: advanced router" and "IP: policy routing" features

I've downloaded the kernel sources, but I don't find any config options with names like these in them.

sudo apt-get build-dep --no-install-recommends linux-image-$(uname -r)
sudo apt-get source linux-image-$(uname -r)

Searching doesn't reveal anything

~/kernelBuild/linux-2.6.35/debian.master$ grep -iR policy . | grep -i routing
~/kernelBuild/linux-2.6.35/debian.master$

So my question is...how can I tell if the kernel I have has these config options. Failing that, how do I build a kernel that does support these things?

Additional use cases for this knowledge. (1) At work with desktop computer plugged into corporate network. Plug 3g phone into USB port. My corporate network wont allow me to access my external servers over ssh, but the 3g phone will. (2) At home on the corporate VPN, but would like to access my other local network computers.

Answer 1

Try

grep CONFIG_IP_ADVANCED_ROUTER /boot/config-$(uname -r)
grep CONFIG_IP_MULTIPLE_TABLES /boot/config-$(uname -r)

The compilation of your own kernel is rather broad theme, and there are plenty of manuals on the internet about it.