Ubuntu

Problem using DHCP and Ubuntu server 9.04

Asked by MK Street

This is an "Ubuntu newbie" question.

I have a school LAN (therefore, onsite "support" means DIY) of Wins PC's (running Win XP).

We have them all configured to use DHCP and have not had any problems. The IP Addrs come from a 3COM switch, as far as I know, on the LAN.

I installed Ubuntu Server vers 9.04 on Monday on one of my (former) Wins boxes. (complete switch, not dual boot).

I first tried to have Ubuntu also use DHCP. But I was not successful. The DHCP communication would go into a never ending loop of DHCPREQUEST, DHCPOFFER, DHCPNAK.

So, I changed Ubuntu to use static IP, and everything was great (or so I thought). I could ping the Ubuntu box from inside the LAN by either IP Addr or hostname. I downloaded Putty and could telnet into ubuntu (by hostname also).

The next thing I noticed was that Wins boxes could no longer connect to the LAN, including my own Wins desktop PC after I rebooted it. The Wins boxes would go into never ending loops of "Acquiring network address". When I switched any Wins box to static IP, everything would be ok for that box immediately for connectivity.

My thought was that the Ubuntu server and the LAN's dhcp server must be dueling it out or somehow in conflict with each other.

I did some limited experiments where I shut down the Ubuntu box, and then an example Wins box was able to get an IP Address and proceed normally.

I cast around the various forums and found info about dnsmasq and it's config file.

I tried adding these lines to my dnsmasq.conf file:

    except-interface=eth0
    listen-address=127.0.0.1
    no-dhcp-interface=eth0

After doing this, I rebooted the ubuntu server.

I also have rebooted the Wins box too.

But it has no effect on the situation.

So I am not really sure what the problem is....help. I am not even sure if i am barking up the wrong tree by looking at dnsmasq.

Thanks!

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actionparsnip (andrew-woodhead666) said : 		#1

If you have a dhcp server implemented, you should disable dnsmasq in the server as this will break the dhcp you already have setup. If a dhcp request hits your serer it may give it some weird IP address.
Otherwise Ive no idea

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MK Street (markenberk) said : 		#2

Ok, sure, ummmm...

how do I configure ubuntu to NOT start dnsmasq? I have looked and didnt see how to do this....

do I need to add to a config file (e.g. /etc/hosts or somewhere) to point to the existing dns server's ip address?
or will ubuntu just discover it on its own "somehow" even with dnsmasq turned off?

thanks

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pablitofuerte (pablitofuerte) said : 		#3

Read this:
https://help.ubuntu.com/9.04/serverguide/C/dhcp.html
https://help.ubuntu.com/9.04/serverguide/C/network-configuration.html

Ubuntu Server Guide (PDF version) https://help.ubuntu.com/9.04/serverguide/C/serverguide.pdf

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krokpeter (stefanharjes) said : 		#4

Hi MKStreet,

I was just dealing with related problems, when I hit your querry. There is always a way to prevent dnsmasq from starting. Just find out which process number it has (first number from the left):
ps -aux |grep dnsmasq
  and then kill it!
sudo kill -15 'process number'

If you want to prevent it from startup, you simply find the executable file (in this case /usr/sbin/dnsmasq) and rename it
sudo mv /usr/sbin/dnsmasq /usr/sbin/dnsmasq-not-wanted

then there is no dnsmasq at boot!

However, I run my laptop in a mixed network with all kinds of operating systems and never ran into this issue.

With best wishes

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