I have a DSL modem hooked up to my Linksys router. I have two computers (OS X and Linux) which have static IP addresses. When I turn my modem off, the two computers can ping each other, and view web pages served from each other. But, SSH and SFTP don't work. It doesn't time out, it just hangs.

I set up SSH on OS X momentarily. When my Linux computer tried to SSH into my OS X computer, it would exchange keys, but would do no more (it asked me if I wanted to accept a new key). When I tried to SSH from the OS X computer to itself, it wouldn't do anything.

When my modem is on everything works fine. Why is this and how can I fix it?