Open and Closed At The Same Time

Dearest Lazyweb:

I have a fair amount of experience with networking, but I have a problem for which I need a solution. I have a broadband line coming in from the cable company. I would like to split the broadband connection into two distinct networks. One will be used for my girl’s business, which is run out of the house. The other will be used as an open network for anyone in the neighborhood to use (please spare me the warnings about having an open network).

As it stands now, I have a router in the girl’s office ( with DHCP turned on and a router in my office ( with DHCP turned off. It basically just acts as an access point. I’ve cabled the house, so there’s wiring between the two routers on opposite ends of the house. I also have an AirportExpress and a third router that I can use.

Thank you Lazyweb!

2 thoughts on “Open and Closed At The Same Time”

  1. There are a couple ways to do this.

    If you can get multiple IP addresses from the cable provider pretty cheap:
    Install a network switch on the LAN side of the cable modem. From there, hang a router off the switch and give it one IP address from the cable company. Then put your home network behind that router using 192.168.0.x addresses offered via DHCP. This router will also act as the firewall to your home network and keep both Internet and open WiFi users out of your stuff at home. Issue a second IP address to the WAP and have it offer DHCP to the open wifi users on a 192.168.1.x range. If the WAP is a WiFi router kind of thing, you can set up the firewall part as you see fit.

    If, for whatever reason, you can only get a single IP address from the cable provider:
    Take one router, give it the outward facing IP and assign the LAN side the address range of 192.160.0.x with no DHCP. Attach a small network switch to the LAN side and connect the WAN/Internet side of the second router. Assign the second router a static outside address of The inside leg will be and offer DHCP to the home network. Set up the firewalling on it to protect the home network from both Internet users and your open WiFi users. The outside interface on the WAP gets assigned, with a default gateway of The WAP can offer DHCP to the open WiFi users as 192.168.2.x.

    There will be some slight changes if the WAP cannot act as a router. Then you’ll have to use the third router in between #1 and the WAP.

    Clear as mud, I’m sure, but that gives you a basic idea how to do it. If this doesn’t make any sense, drop me an email and I’ll crank off a quick network diagram for each scenario.

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