RogerBW's Blog

I don't like network-manager. It's too big and complicated and hard to persuade to do the things I want. Fortunately it's not too hard to do without it.

This is all for Debian/wheezy. It'll probably apply to other versions too. It certainly works on Raspbian for the Raspberry Pi.

For wired networking, it's really easy. In /etc/network/interfaces put in either a static address:

allow-hotplug eth0
iface eth0 inet static
        address 10.0.0.3
        netmask 255.255.0.0
        network 10.0.0.0
        broadcast 10.0.255.255
        gateway 10.0.255.254

(I don't think you actually need the network and broadcast lines any more, but back in the day they were helpful.)

Or for DHCP:

allow-hotplug eth0
iface eth0 inet dhcp

No problem. Use ifup and ifdown to bring the interface up and down. (If you want to do this as a normal user, sudo is the easiest way.)

For wireless it's only slightly more complex. You'll need the wpasupplicant package, and to build a configuration file for it, let's say /etc/wpa_supplicant.conf. Set up a separate stanza for each network you want to connect to, with a different id_str entry for each different set of things you want to do with the connection. (I'll come back to this.)

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
#
# home network; allow all valid ciphers
network={
        ssid="my_homenet_ssid"
        key_mgmt=WPA-PSK
        psk="my_homenet_password"
        id_str="home"
}

network={
        ssid="some_other_ssid"
        key_mgmt=WPA-PSK
        psk="my_remote_password"
        id_str="mobile"
}

network={
        ssid="open_network_ssid"
        key_mgmt=NONE
        id_str="mobile"
}

You can add scan_ssid=1 to a stanza if you need to connect to a network that doesn't broadcast (but this makes your device leak information about which networks it's looking for, which is very easy for an attacker to spoof, so don't configure your APs this way if you have the option). If you're willing to connect to any open network, just leave out the ssid line in that stanza. If you're connecting to WPA-Enterprise and other more complex setups, see the wpa_supplicant.conf(5) man page for how to set up certificates and such.

Then in /etc/network/interfaces set up a stanza for each id_str:

iface wlan0 inet manual
        wpa-roam /etc/wpa_supplicant.conf

iface home inet dhcp

iface mobile inet dhcp

Why did I put in separate home and mobile entries? Because you can tag other things onto the definitions: under the mobile entry, I have:

        post-up /etc/init.d/openvpn start
        pre-down /etc/init.d/openvpn stop

to set up my VPN connection to the home network automatically. The end result is that I can connect seamlessly to my servers at home from my laptop wherever it is, using the VPN automatically when it's needed.

If you have a wireless network without DHCP, which is quite rare but not un-heard-of, you can use inet static as mentioned above for wired networks. Just give it a different id_str in /etc/wpa_supplicant.conf and then add something like:

iface special_flower inet static
        address 10.20.30.99
        gateway 10.20.30.40
        netmask 255.255.255.0
        dns-nameservers 10.20.30.40

That dns-nameservers directive needs the resolvconf package, which is probably a good idea anyway if you use anything other than DHCP.

If you want more control of when you connect to specific networks, such as being able to enable or disable entries in the list, put your main user in the netdev group and install wpa-gui.