Difference between /etc/network and /etc/NetworkManager in Ubuntu

Question

I use Ubuntu 12.04.1.

I understand networking, and the meaning of files in both folders, but the question is:

"How are they coexisting?"

For example, if I have this configuration of eth0 in /etc/network/interfaces:

auto eth0
iface eth0 inet static
address 192.168.0.2
gateway 192.168.0.1
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255

and this one in /etc/NetworkManager/system-connections:

[802-3-ethernet]
duplex=full
mac-address=00:1E:33:71:CD:A4

[connection]
id=eth0
uuid=4c12ff66-028a-4338-bad5-fa6e9c5e6939
type=802-3-ethernet

[ipv6]
method=auto

[ipv4]
method=manual
dns=192.168.0.1;
addresses1=192.168.0.1;24;192.168.0.1;

What will be the resulting address of the interface, 192.168.0.1 or 192.168.0.2, and why so ?

Answer 1

/etc/network is what your Operating System uses to assign network addresses. NetworkManager is what Ubuntu (and other distros like RedHat) use to force /etc/network to do its bidding. It will automatically configure the network services. Many implementations now do not allow NetworkManager to override /etc/network settings. NetworkManager used to really bugger things up in a server environment.

So in short, /etc/network is for manual configuration of the network. /etc/NetworkManager is for automatic configuration of the network addresses. It's useful for laptops or other PCs that change networks a lot. Tends to be a headache in a server environment, so many disable NetworkManager and just run with /etc/network