as usually, I end up answering my own (painfull, not google-able) problems.
so, I was too concentrated on DNS (that being the only service I actually needed to work right) that I did not bother testing any other services. After doing a lot of rtfm-ing on the linux routing and packet filtering and trying out all sorts of things I decided that until I find a solution, to make the DNS work. long stroy short, I configured my DNS to bind to each interface and it was than when I saw that power dsn can actually change the source address in the packet. So I got DNS working and then I figured I should try another service, http. I did the test without lartc implementation, it behaved as described, packet went out the wrong interface. however, when I implemented the lartc split, it went on the right interface.
So the actual problem was not the lartc but the powerdns. maybe I should log a bug with them.
so for whoever searches for a similar problem: make sure your service is not messing up the packets to begin with. test your setup with a nice playing apache for example and if that works, it’s definitelly your service to blaim.
