network issues

**Kanefa** · October 27th, 2013

I may not understand. Before and after running the commands the IP address is "192.168.2.27" which is wrong.

I'm also not sure the issue is whether the MAC is whitelisted or not. The Dell's all ran Windows in the lab and had no problems. We still have one that continues to run Windows and it continues to work. Whether or not the computers are whitelisted the problem only arises when I put Lubuntu on the computer. Regardless, it may be a smart idea, but is that the problem?

**The Cog** · October 27th, 2013

@steeldriver: I just double-checked with tcpdump, and the server does indeed reply from source port 67 to the client destination port 68.

I also double-checked the iptables rules, and it seems that dhclient gets access to the packets before they go through iptables. dhclient -v continues to show the packets arriving from the rogue server, and the counters in iptables don't show any packets hitting the rule. As such, I guess the dhcp client is connected somewhere in the packet processing before iptables (much as tcpdump is) and we will not be able to prevent the client from seeing responses from the rogue server. Forget using iptables.

It is possible to tell the client to talk to a specific server, like this:
sudo dhclient -v -s 192.168.11.1 eth0
but when I try that here, my server does not respond, so it may not help you either.

You may get lucky by calling "dhclient -r eth0" and "dhclient -v eth0" repeatedly until you get a lease from the right server.

And as steeldriver says, the 192.168.11.1 server seems to be sending DHCPNAK which is a negative response - it is refusing you for some reason. This may be because you didn't release the 192.168.2 lease first, I don't know for sure. But you may really need to talk to the network admin to get this resolved.

**steeldriver** · October 27th, 2013

@The Cog - sorry for the misdirect, thanks for clarifying

**The Cog** · October 27th, 2013

Got it!
Release the bad lease with

Code:

sudo dhclient -r eth0

Then edit /etc/dhcp/dhclient.conf and add this line:

Code:

reject 192.168.2.1

and from now on, you should ignore that rogue server.
Run:

Code:

sudo dhclinet -v eth0

to (hopefully) watch it choose to ignore the rogue. Now you just have to worry about the DHCPNAK from the good server.

Edit:
It appears that you can also use the format "reject 192.168.2.0/24" which would reject any dhcp server on 192.168.2.*.