Networking :: Unable To Ssh Without Dropping Firewall Security On Dsl Modem?

I have a home network with a linux dhcp server and a couple of clients. The Internet comes from a dsl modem with a different subnet than my wireless router. The network works fine and I have no problems, but I now need to ssh to a work computer and the only way I can do that is if I drop the security in my dsl modem. So I thought all I need to do is use port forwarding on my dsl modem, but it won't let me because it is on a different subnet. I tried putting the dsl modem on the same subnet, but that did not work and made it so I could not access anything.