It's on a laptop running Ubuntu 14.04, where the WiFi `wlan0` is used to connect to Internet. 

And `eth0` (RJ45) is set statically in `/etc/network/interfaces`

```
auto eth0
iface eth0 inet static
    address 192.168.11.168
    netmask 255.255.255.0
    gateway 192.168.11.100

```

The problem is, there is usually no cable connected to `eth0`, so at boot the IP address is not set. And when a cable is connected (on a LAN) for a short period of time, the address has to be set

```
ifdown eth0
ifup eth0

```

and since the device the laptop connects to does stop and restart, the IP is lost and has to be set again. 

That kind of configuration does not seem to fit for a laptop connecting at times to devices, which may reboot etc... 

Is there a way to tell the system to keep that IP assigned to `eth0`, whatever happens, cable disconnections, boot, etc... ?

**edit**

It seems *wicd* was the culprit. Once I removed eth0 from its config, the IP address behaved more consistently. It's always ON, on boot, unplugged... I knew the good old *interfaces* file could be trusted!