The main problem is making a connection between your parent's network and your network. I'm assuming they are two physically separate areas.
I may have implied it but didn't specifically mention it. Yes, these are on two different physical networks.
This can be worked around by setting up some sort of VPN tunnel between the two routers. This is the simplest way, and it gives you the most options. With a VPN, it would be a route entry on the router.
You could go with SSH tunnels, but things get messy if the clients are Windows due to Windows not having most of the needed tools to really take advantage of it.
SSH tunnels are an option. The CrashPlan FreeNas plugin essentially builds the sshd tunnel from my understanding and the client connects via the crashplan desktop tool. I will explore this option a little more.
The next problem is throughput, as Flying Fox mentioned.
Upstream bandwidth is a problem. Cox may not throttle like some, but they aren't going to prioritize outbound traffic either. They've also started nagging people about reaching usage caps, so they may, or may not, start clamping down on "excessive usage" even though they don't mention usage caps in any of their advertising.
Good point. I wouldn't think that I would get close to any caps, but I suppose that is an options. The initial backup will be a physical external drive that I load from, then incrementals will stream online (which really shouldn't be a whole lot I'm thinking).
Finally, dynamic IPs and firewalls.
Unless you're paying for a business class line, you're going to have a dynamic IP, many ports will be filtered, and this would be in violation of the ToS. None of these are really problems, but they will make things harder.
Noted! I am using duckdns for my dynamic IP addressing without issue for a few other things right now. I'm familiar with maintaining the ports on my router and redirecting them if needed. I will check on the ToS to see if this type of thing is frowned upon.
Thanks for the link! Do you know if Crashplan allows internet backups to another PC? I know it does LAN, but not sure on WAN.
Maybe you could set up Owncloud on your server and install the client on your parents' computers.
This is probably my leading option right now. It looks like a pretty neat tool! Do you have any experience with it that you could speak to? I would assume that once I get my port forwarding setup, it is open to WAN devices for connecting as well (such as my phone at work, my parent's desktop on their network, etc)?