IPROUTE2 is your friend

I've lost several hours on the multiple uplink in a single machine problem, tried several tutorials & How-To (most of them including iptables mangle marks crap), but discovered this simple and objective document about IPROUTE which sorted it in few simple lines:

http://lartc.org/howto/lartc.rpdb.multiple-links.html

Thank you, LARTC guys.