wlan0 won't connect unless eth0-wire is connected

Question

I want to change network interface on my home server, from a wirebased (eth0) to a wireless (wlan0) using a USB-wlan card. I've installed the RT73-drivers using http://ubuntuforums.org/showthread.php?t=400236 and it seems to be working.

My problem is that wlan0 only works when the wire for eth0 is connected. As soon as I disconnect the wire, the wireless interface goes down.

I'm guessing that it has something to do with my /etc/network/interfaces so here it is:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
        address 192.168.1.19
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 192.168.1.1
        dns-search workgroup

auto wlan0
iface wlan0 inet static
        address 192.168.1.20
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
        dns-nameservers 192.168.1.1
        dns-search workgroup

        pre-up ifconfig wlan0 up
        pre-up iwpriv wlan0 set AuthMode=WPAPSK
        pre-up iwpriv wlan0 set EncrypType=TKIP
        pre-up iwpriv wlan0 set WPAPSK=MY_PASSWORD
        pre-up iwpriv wlan0 set SSID=MY_SSID
        pre-up iwpriv wlan0 set NetworkType=Managed

Both interfaces are connected to the same router.

I'm running Ubuntu Server 8.04

Answer 1

My problem is that wlan0 only works when the wire for eth0 is connected. As soon as I disconnect the wire, the wireless interface goes down.

Because your wireless interface is not working to begin with.

For one, you've set it up completely wrong.

change all the pre-up commands to just

wpa-ssid MY_SSID
wpa-psk MY_PASSWORD

then see where you stand.