How to Stop Ubuntu 11.10 Wireless Dropping Out

Unfortunately Kubuntu and other Ubuntu 11.10 versions are currently (October 2011) suffering from a wireless bug which is causing wireless to drop out.

I’ve been running my wireless access point up until now with WEP encryption, mainly to keep compatibility with older wireless equipment. In case you think I’m mad, the access point spends most of its time switched off and therefore is more secure than WPA!

Initially, I changed the MTU setting to 1500 from Auto (see instructions below) to see if this would fix the problem. Whilst it did not fix it it did get more reliable. Although I could not reconnect as I got an authentication failure

Looking deeper into the problem I noticed in the log files that the wireless was trying to authenticate using WPA and not WEP encryption. This would explain why it could not reconnect even if I reset networking and disabled/ enabled wireless.

As a matter of elimination I changed my access point to WPA-PSK authentication and then changed Kubuntu’s settings and authentication password.

This seems to have resolved my particular problem, which appears to be a bug in how WEP wireless connectivity is handled after a disconnect. 

My laptop is an aging Dell Latitude C640 with an Intel Pro Wireless (IPW2200) wireless G card.

How to change the MTU setting

The MTU (Maximum Transmission Unit) setting for Ethernet should be 1500 bytes.



16 Mbit/Sec Token Ring


4 Mbits/Sec Token Ring






IEEE 802.3/802.2




In Ubuntu this is set to automatic in Network Manager and I suspect this is where the problem arises.

To change the setting in Network Manager:

  1. open Network Manager
  2. Select the Wireless tab
  3. Select your connection
  4. Choose Edit
  5. At the bottom of the page is the MTU setting, enter 1500
  6. Click OK
  7. Exit

or follow these instructions

If you just want to test you can enter from terminal the following command in the format

sudo ifconfig nwif mtu #

where nwif is the network interface name e.g. eth0

# is the MTU number


sudo ifconfig eth1 mtu 1500

If you then wish to permanently store this MTU setting, then from Terminal edit as sudo


and enter as the last line under your network interface settings:

mtu 1500

Below is an example of how it might look

iface eth0 inet static





mtu 1500

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5 thoughts on “How to Stop Ubuntu 11.10 Wireless Dropping Out

  1. I installed a new ubuntu 11.4 server. All installed well but after I log in I get an error message cannot write, read only file. Even when I sudo or su -i to root. I cannot update anything. How can I correct this error and get write permission?


  2. Hi,

    Thank you very much for this nice tutorial.
    I have the same problem where my wifi connection randomly drop out.
    I am using notebook HP DV3 with Centrino Wireless-N 1000 card.

    This is only happen if I use battery on my laptop. Or even battery and power cable is plugged in, there still wireless problem, not steady connection. Randomly drop after 5 – 10 minutes.

    If I only use power cable, then the problem disappear, gone with the wind blow !!
    Dunno why.

    I already follow the above instruction to change the MTU in network manager and now after 10 minutes, I still have my wireless connected.


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