Problems with wlan connection via dhclient in Squeeze

["Astrid Jürgensen" <astrid.jurgensen@gmx.de>]

Hi,

I recently upgraaded the operating system of my laptop from Debian Lenny 
to Debian Squeeze. Since then, I have some problems connecting to the 
internet using dhclient.

1. When I try to set up a wlan connection (wlan0) manually by typing 
dhclient at a command line, I get no connection and the following message 
on screen:

	Internet Systems Consortium DHCP Client 4.1.1-P1
	Copyright 2004-2010 Internet Systems Consortium.
	All rights reserved.
	For info, please visit https://www.isc.org/software/dhcp/

	No broadcast interfaces found - exiting.

I can connect to the internet using an ethernet cable (eth0), getting the 
following message on screen:

	Internet Systems Consortium DHCP Client 4.1.1-P1
	Copyright 2004-2010 Internet Systems Consortium.
	All rights reserved.
	For info, please visit https://www.isc.org/software/dhcp/

	Listening on LPF/wlan0/xx:yy:zz:xy:xz:yz
	Sending on LPF/wlan0/xx:yy:zz:xy:xz:yz
	Listening on LPF/eth0/xx:zy:xz:yy:yz:zz
	Sending on LPF/eth0/xx:zy:xz:yy:yz:zz
	Sending on Socket/fallback
	DHCPREQUEST on eth0 to 255.255.255.255 port 67
	DHCPACK from 192.168.2.1
	bound to 192.168.2.101 -- renewal in 134470 seconds.

Curiously, once I have established the eth0 connection, if I then pull the 
ethernet cable and run dhclient again, I can connect via wlan (wlan0). The 
following message appears on screen when I do so:

	Internet Systems Consortium DHCP Client 4.1.1-P1
	Copyright 2004-2010 Internet Systems Consortium.
	All rights reserved.
	For info, please visit https://www.isc.org/software/dhcp/

	Listening on LPF/wlan0/xx:yy:zz:xy:xz:yz
	Sending on LPF/wlan0/xx:yy:zz:xy:xz:yz
	Sending on Socket/fallback
	DHCPREQUEST on wlan0 to 255.255.255.255 port 67
	DHCPACK from 192.168.2.1
	bound to 192.168.2.103 -- renewal in 135404 seconds.

What parameters do I have to change, in order to connect via wlan without 
connecting via ethernet cable first?

2. Looking through the various log-files (syslog, dmesg, ...) I noticed 
that the system tries to automatically connect to the internet 
continuously even when there is no connection available. How do I turn 
this off?
I only want the computer to search for and connect to the internet, when 
I specifically tell it to do so.

Thank you very much in advance for your assistance.

Cheers,
Astrid.
.