I have a laptop with Ubuntu 11.04. Failed to connect my home wireless network, which is composed of a modem and a Netgear router. 

ifconfig showing:

```
wlan0     Link encap:Ethernet  HWaddr 00:24:d6:07:2b:a2  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:30238 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24005 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:26945081 (26.9 MB)  TX bytes:3169731 (3.1 MB)

wlan0:avahi Link encap:Ethernet  HWaddr 00:24:d6:07:2b:a2  
          inet addr:169.254.6.188  Bcast:169.254.255.255  Mask:255.255.0.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1

```

iwconfig showing :

```
wlan0     IEEE 802.11abgn  ESSID:"mywirelessnetwork"  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=15 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off

```

I do not quite understand how the virtual interface wlan0:avahi appeared. My guess was, my request `sudo dhclient wlan0` failed to get a valid ip, although I did not get any error message from running that command. I executed `sudo dhclient wlan0` again, but still no error message or network connection.

Later today, I tried to connect to a public wireless network. Still got the same error. But when I reboot my machine, no such problems.

I am confused by the wired situations. Is there anything wrong with my network configuration? What should I do if I encounter similar problems in future?