Here's my "problem". I live near my school, and I can pick up a very good wireless signal, I would like to use its high speed connection as much as possible. I also have cheap dsl, which is not very fast.

The school naturally has a bunch (almost all) ports blocked, so I would like to use the dsl for apps that need certain ports, and the schools connection for things like ftp.

I'm considering going out and buying a second nic. My question is, suppose that I get both nics to work, one connected to school with ip 1.1.1.1 and the other connected to dsl with ip 192.xxx.xxx.xxx behind router with ip 2.2.2.2 .

Is there a way to tell programs which nic they need to use? For instance, I want to be able to ssh into my machine from somewhere else, which means I would need port forwarding, which means I would need to ssh to the dsl assigned IP. Then, while remotely logged in, I want to be able to use ftp over the schools much faster connection.

If anyone can point me in the right direction I would be thrilled.

It is easy to route based on destination. Find the IP address of your FTP destination then add a route that directs it over the schools Gateway. You can make it permanant or temporary but all services will be routed for that address while the route is active, not just FTP.

That is a good idea, but what about applications like bittorrent? I don't want it to get confused as to which nic to use, because that would kill its performance.

Can I add a default gateway, say the dsl line, so that bittorrent will be sure to use it no matter where I'm trying to connect?

You should have the default gateway and that will be used for everything that is not explicitly routed. The explicit route(s) will take precedence for the defined destinations for all services.

In addition to assigning using plain-old routing tables, you can also use iptables to mark packets, and later use those marks for routing. You can use l7-filter for “smart” matching (to regular expressions or magic bytes), but if you are doing bittorrenting yourself, you probably already know the port, so you can mark based on that.

use l7-filter for “smart” matching ,have to say looks very good ..