Chancing IPs

[Tom H]

On Wed, Nov 4, 2009 at 6:42 PM, Tom H <tomh0665 at gmail.com> wrote:
> 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).

You can also check whether it is a dhcp problem with
# grep -i "no dhcpoffers" syslog*