How to extend WIFI from ethernet
You just need a wireless router that supports AP mode, lets you turn off its DHCP server, or can be set to a seperate DHCP range. There's also standalone access points - which might be the cheapest option.
In my case I have a primary router (connected to a ONT for fibre optic internet) connected to a Asus router that has AP mode support.
In the past I've used
- A WRT54GL with DHCP turned off but no 'AP mode' to speak of with three consumer routers - one acting as a router (dlink of some sort), one in AP mode (asus), and one with DHCP turned off(WRT54GL/DDWRT), one network setup. The WRT failed, and you can see a detailed description of the setup in this question.
- A wierd 2wire ADSL modem router that wouldn't let me turn off DHCP, I used a different IP address range, and the horrible hack that is double nat. That did isolate the two networks. The set up even extends to triple nat - I tested a 192.168.1.x subnet connected to a 10.0.0.x subnet inside a 192.168.1.x subnet for... complete horror.
Things to look out for.
In general with AP mode or DHCP turned off you need to connect two 'regular' ethernet connectors on either AP. Don't use the 'internet' ethernet connector there (I have an answer explaining this somewhere, but I can't find it).
Make sure your 'AP' has a fixed known IP address, preferably outside your DHCP range, so that you can find it if something breaks.
Have different SSIDs so you know you're on the right AP.
A Wireless Access Point or a router configured as such.