dhclient overrides nameservers in resolv.conf

Binary package hint: network-manager

Using the "Manual Configuration..." dialog of KNetworkManager, set up your network connection (in my case, wlan1):
- use the "Configure Interface" button to produce the dialog called "Configure Device wlan1 - KDE Control Module"
- In this dialog, choose "Automatic - DHCP" and check "Activate when the computer starts" - then OK that dialog
- Choose the "Domain Name System" tab
- Enter two domain name servers, e.g. 1.2.3.4 and 5.6.7.8
- Press Apply or OK

Your network connection will be brought up, but the chosen Domain Name Servers are not used. Instead, the DNS provided as part of the DHCP negotiation is used instead.

In order to fix this, I have added the following line to my /etc/dhcp3/dhclient.conf:

supersede domain-name-servers 1.2.3.4,5.6.7.8;

This prevents the dhclient from overriding my settings, and everything else about DHCP is unchanged.

So, KNetworkManager should add the equivalent line to /etc/dhcp3/dhclient.conf in this situation (dhcp enabled, but name servers provided by the user). Though usually just annoying (e.g. my home black-box router has a broken DNS server), this is _potentially_ a security problem indirectly, since many home routers are vulnerable to being attacked, which could, for example, allow their built-in DNS to be poisoned.