You are using a modem that doubles as a nat wireless router right? I can almost guarantee the problem is the router portion of the modem. Maybe you can hard reset it (or WOW_Dan can) and someone can provide you with a password to set it up the way you want to. But if it still causes your ssh connections to drop after a hard reset, you need to bridge the modem. This will effectively disable the router portion and you can get your own router which will surely work better. For whatever reason the software running on these is junk. And yes, I am speaking from experience, as I've had a similar arris modem in the past, albeit with a different isp, but the same exact ssh problem you are describing. You are using ssh and unix servers, I'd expect you'd to be running a router with dd-wrt or openwrt already anyways.