DHCP is very unreliable.

I'm using a D-Link DWL-G122 USB wireless dongle with Karmic. I have removed network manager (causes me all sorts of other problems), and am configuring the network using the /etc/network/interfaces file. I find that ubuntu is able to associate this wireless dongle with my access point. However, it cannot reliably get a DHCP lease. After boot, although the wireless is associated, attempting to ping the router results in the message "network is unreachable" (or similar). If I run the command /etc/init.d/networking restart, often dhcp fails to receive a lease (although, sometimes the command works), with results as follows:

andrew@andrew-desktop:/etc/init.d$ sudo /etc/init.d/networking restart
 * Reconfiguring network interfaces... There is already a pid file /var/run/dhclient.wlan0.pid with pid 3493
killed old client process, removed PID file
Internet Systems Consortium DHCP Client V3.1.2
Copyright 2004-2008 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/sw/dhcp/

Listening on LPF/wlan0/00:15:e9:a3:8c:13
Sending on LPF/wlan0/00:15:e9:a3:8c:13
Sending on Socket/fallback
DHCPRELEASE on wlan0 to 192.168.1.1 port 67
Error for wireless request "Set Mode" (8B06) :
    SET failed on device wlan0 ; Invalid argument.
Internet Systems Consortium DHCP Client V3.1.2
Copyright 2004-2008 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/sw/dhcp/

Listening on LPF/wlan0/00:15:e9:a3:8c:13
Sending on LPF/wlan0/00:15:e9:a3:8c:13
Sending on Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 10
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 17
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 16
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 6
No DHCPOFFERS received.
No working leases in persistent database - sleeping.
                                                                         [ OK ]

I have seen other people in forums with seemingly similar problems, and they have suggested such things as stopping apparmor, which I have tried, and it does not seem to make a whole lot of difference! They also suggest adding a line:

        pre-up sleep 10

after the line

iface wlan0 inet dhcp

in my /etc/network/interfaces file, but I'm not sure this make much difference either.

Thanks,

Andrew Walsh.

ProblemType: Bug
Architecture: amd64
Date: Mon Nov 2 20:41:16 2009
DistroRelease: Ubuntu 9.10
ExecutablePath: /sbin/dhclient3
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
Package: dhcp3-client 3.1.2-1ubuntu7
ProcEnviron: PATH=(custom, no user)
ProcVersionSignature: Ubuntu 2.6.31-14.48-generic
SourcePackage: dhcp3
Uname: Linux 2.6.31-14-generic x86_64
XsessionErrors:
 (gnome-settings-daemon:1551): GLib-CRITICAL **: g_propagate_error: assertion `src != NULL' failed
 (nautilus:1584): Eel-CRITICAL **: eel_preferences_get_boolean: assertion `preferences_is_initialized ()' failed
 (polkit-gnome-authentication-agent-1:1609): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed