Chancing IPs

[Tom H]

On Wed, Nov 4, 2009 at 1:43 PM, Aart Koelewijn <aart at mtack.xs4all.nl> wrote:
> in my network I have an old laptop with Ubuntu 8.04 running 24/7 for a
> measurement project. This laptop has a WiFi connection with my router.
> Normally it will get an IP from the DHCP range off the router,
> 192.168.nn.mm. This is always the same IP. But every so often, perhaps
> after a week or two weeks it will change its IP to 169.254.7.206 and it
> will lose its connection to a database outside my home where the data are
> combined with data from other places. The data of course are still saved
> in a database in the laptop itself. I also have a ssh-connection from my
> desktop to this laptop to monitor what is happening on the laptop. This
> connection is lost too.
> I wonder how this change of IP can take place and how I can pretend it.
> As the best the laptop can do is a web-64 protection and the least the
> router will accept is a web-128 protection the wifi connection is
> unprotected. The router will only check if the mac-address is one of the
> allowed mac-addresses.

It must be your dhcp lease that is expiring and is having trouble
being renewed because a 169.254.x.x address is self-assigned when when
a dhcp lease cannot be acquired.

Your dhcp lease must be one-week long and the renewal must be failing
from time to time. You can check the length of your lease with
# ps -ef | grep dhc
and then looking at the contents of the lease file (defined after the
"-lf" in the output of the command above).