Hi there,

Where I work, we're starting to investigate using Linux as a desktop platform (at the moment we're testing using Ubuntu), instead of Windows. However, a lot of our users have laptops, and we're having a strange problem with DCHP.

We have our lan split into different subnets; so for example, our finance department might have have IP addresses in the x.x.160.x range, while our IT department might have addresses in the x.x.64.x range, etc..

If a laptop is connected to the network when it boots up, it'll pick up an appropriate address via DHCP just fine. If you pull out the network cable, the machine detects that it's disconnected (verified by the Network Monitor panel applet). However, if we then take that laptop and reconnect it to the network from a connection in a different subnet, while the machine detects that it's reconnected, it doesn't automatically renegotiate a new address via DHCP, and attempts to use the old one.

If we do a manual release/renew using 'sudo ifdown eth0' followed by a 'sudo ifup eth0', then we get a valid new address fine; but the machine won't do this automatically.

I've had a look around via Google, but haven't found anything useful. Is there any way to set this up?

Thanks for your help!


John

dhclient eth0
should grab an address automatically from your subnet's DHCP server. Thats a one step process. Otherwise you could put that into a shell script if you wanted to clickety-click.
Regards
Chris

Is there any way to get Linux to automate this though? I mean, for example under Windows, if a network connection has been disconnected, and then reconnected, Windows will go and contact the DHCP server to request a new address automatically - the user doesn't have to do anything, and after a few seconds their computer is up and working again, regardless of what subnet they're now connected to.

Is there any way to do that in Linux?

Thanks again!

Thats odd, I have a dhcp server set up on my RedHat 9 box. It seems to be reassigned IP information whenever its disconncted(same goes for my WinXp computer). Maybe double check your dhcpd.conf file?

my 2 cents

Haven't use this myself ( no laptop ) but have a look at ifplugd

stakhous: Well in our case we're not running DHCP servers directly on the client machines - this problem is definitly something in the local Linux setup on each laptop.

homey: Thanks a million! Just downloaded and installed ifplugd, worked like a charm! If anyone else is having the same problem we are having, I recommend giving ifplugd a go, worked flawlessly here

Cool Beans!