Receive Wi-Fi via dongle, redistribute via Airport My house has standard broadband internet. A coaxial cable comes into the house from the road. Attached to this is a wireless router.

My room is right at the other end of the house.  I can only get a decent signal by putting a USB Wi-Fi dongle out of one window.

As I have a spare old MacBook, I'm attaching the dongle via a 3m USB extension cable, and putting it out of the window.

I am then configuring this old MacBook to redistribute the Internet, using its internal Wi-Fi card,  i.e. the airport.

Other devices can see this new Wi-Fi spot and connect to it.  Primarily my new MacBook Air.

But trying on the browser, it fails to load a webpage. 'ping' from the command line fails to resolve www.google.com.

Now here is the weird thing. It has been working on occasion. I don't know if it's the result of my fiddling around.

I've tried quite a few things: I've tried using Bluetooth to redistribute. I've tried setting the IP address for the airport manually. I've tried altering the channel. Probably a few more but I'm not comfortable thrashing around not knowing what I'm doing with no clear gameplan.

Could someone please give me a sequence of moves to tackle this?
It sounds like you're trying to NAT behind your old Macbook. I assume you're using Internet Sharing (System Preferences -> Sharing) to do so, which will auto-configure a NAT for you.

If you are able to connect to the Macbook's shared connection at all you should check the routing table of the machine you are connecting to the Macbook NAT from. You might have a duplicate route, or traffic might be going the wrong way.

You can do this via Network Utility (GUI for netstat). In Network Utility on your client machine go to the Netstat tab, click the radio button "Display routing table information", and then press "Netstat".

If you run an ifconfig on your Macbook, the IP of a secondary interface (br0, tun0, etc OR your internal card - NOT your wifi dongle) should be a local IP - i.e. 192.168.x.x or 10.0.x.x. Ensure that the default gateway in your client machine's routing table is the same as the IP of the network interface that corresponds to your shared connection.

You can change the default gateway via the "Network" System Preferences pane, or using the route command, i.e.

route delete default
route add default &lt;Macbook ip&gt;