Traditionally configure wlan?

[Josef Wolf]

Hello,

I am trying to configure wlan without the use of networkmanager. I want to
do that with the traditional method for two reasons:

1. The wlan interface should go up automatically even when nobody is logged
   in (so networkmanager is not even running)
2. I prefer to configure my systems automatically (with a system similar to
   cfengine)

I have tried google, but there is lots of (contradictory) information out
there. So google just added to the confusion instead of being helpful :-(

What I want to achieve is to be able to connect to multiple access points
via WPA2 and different ESSID's (e.g home, work, wherever). In addition, I'd
like the wlan to go down automatically when eth0 goes up and go up again if
eth0 goes down.

I see that I can set essid/mode/channel/keys vial iwconfig. But I guess I
should not do that manually and use wpa_supplicant to do that for me.

AFAICS, wpa_supplicant is able to connect to multiple APs and reconnect to
another if the AP disappears (according to the priority in its config file).

But I don't see how to shut down wlan when eth0 comes up (and vice versa).

Next problem is that the documentation is not very clear where the
wpa_supplicant.conf file should be located, and the wpasupplicant package
does not contain such a file, so how do I know where to create it?

Second question is, how do I make sure that only WPA2 is used? And how do
all those acronyms (TKIP/CCMP/RSN/whatever) impact security? Can anyboy
point me to some overview?