I have a lousy 3801HGV modem/router that I have to use with AT&T UVerse. Due to AT&T issues, that router does not allow the ability to change DNS settings. I have added a LinkSys E1200 as a second router in order to use OpenDNS settings (to filter content to my kids). I still have machines that I want to run on the 3801 and they sometimes need to communicate with machines behind the E1200. The problem is that the 3801 doesn't seem to allow any sort of static routing. Let's say I wanted to do file sharing with two machines behind the E1200. Any thoughts on how to configure that?
You'd be better off rethinking your entire solution, there are no winners in meddling with ISP firmware.
What I do is have my computer connected to both devices at once, (windows lets you configure adapter priority in the advanced settings of ncpa.cpl , so you can choose which network card will be the default route for internet requests). Therefore my family is setup on one router, and I'm on both, default route no filtering, but they can access my shares, and we can play multilayer LAN Games, etc.
Forget about your ISP modem. It's about as useful as a paper-weight.
I would recommend, and can comment that this works, buying 2 Linksys routers and install DD-WRT on them. I have found that residential routers either have internal static routing disabled or broken. After I installed DD-WRT - everything worked great. This would work great if you have 2 public IPs, if not then you will need to set the gateway of router 2 to router 1.
[ This is a question for the network experts - if you set the gateway of router 2 to router 1 - do you still need static routes? ]
Router 1 - 192.168.1.X
Router 2 - 192.168.2.X
Then using DD-WRT you can set static routing between the subnets.
What you really want is a proxy. I know of a co-worker who uses IPcop ( http://www.ipcop.org/2.0.0/en/admin/html/ ) - although it may be overkill for this situation. I think all you need is squid setup to filter out keywords you don't like ( http://en.wikipedia.org/wiki/Squid_(software) ). I'm sure it could be setup as a service so all you need to do is tell your kid "if you want to surf just turn on this computer".