I have a laptop with two wired network cards. One of them is the builtin card and the other is a USB NIC. I use the USB card because the builtin one has a strange problem I haven't been able to solve (in both Windows and Linux).
Anyway, when I first installed Ubuntu 10.04 I had some problems with the Network Manager software. I had to use the same MAC on both the wired cards because my ISP's DHCP server used the MAC to assign IPs. NM refused to "work with" the second NIC. I was in a hurry and I replaced Network Manager with wicd. I've been using wicd until a few days ago when I decided I have to make NM work because I'm getting ready to install Ubuntu 11.10 on my new laptop. Meanwhile I changed my ISP and the NICs have different MACs.
After I reinstalled NM it showed me the "device not managed" message for both my wired NICs. I tried all the solutions I could find on the internet but none worked.
Here's how I solved the problem:
1. Run "sudo gedit /etc/network/interfaces" in a Terminal window.
- replace gedit with your favourite text editor
- the interfaces file should look like this:
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet loopback
auto eth1
iface eth1 inet loopback
2. Delete (or commennt with #) everything in the interfaces file except
auto lo
iface lo inet loopback
- this is the loopback interface
- NM will refuse to "manage" any network interface that has configuration options in this file
3. Go to Synaptic Package Manager and COMPLETELY Remove network-manager and network-manager-gnome packages
4. Restart
5. Now you probably don't have an active internet connection
Run "sudo dhclient eth0" in a Terminal window. Replace eth0 with the network interface you get your internet connection from. You can run "ifconfig -a" to see the names of your network interfaces. The DHCP client should acquire an IP address for your Network Interface.
6. Now reinstall Network Manager with Synaptic or Ubuntu Software Center or the command line.
7. Restart
8. Tada. Network Manager should now "manage" all your netwrk connections.
P.S.0 I'm starting to miss wicd. You could configure it to prefer a certain wired NI or to prefer the wired interfaces over the wireless ones.
P.S.1. If you now a faster way to make NM reset it's settings after step 2 please leave a comment. Thanks.
