Network Configuration

All of this configuration will happen automatically if you choose Yes, configure /etc/network/interfaces in the Setup wizard. If for some reason you need to configure /etc/network/interfaces manually, you can do the following.

NOTE! You may lose network connectivity during this process! Have a backup plan if attempting over SSH!

Stop Network Manager:

sudo /etc/init.d/network-manager stop

Prevent Network Manager from starting at next boot:

sudo mv /etc/init/network-manager.conf /etc/init/network-manager.conf.DISABLED

Next, configure your network interfaces in /etc/network/interfaces.

Management interface

You’ll want a management interface (preferably connected to a dedicated management network) using either DHCP OR preferably static IP.

Sniffing interface(s)

You’ll want one or more interfaces dedicated to sniffing (no IP address). NIC offloading functions such as tso, gso, and gro should be disabled to ensure that Snort/Suricata get an accurate view of the traffic (see https://blog.securityonion.net/2011/10/when-is-full-packet-capture-not-full.html).

Sample /etc/network/interfaces

auto lo
iface lo inet loopback

# Management interface using DHCP
auto eth0
iface eth0 inet dhcp

# OR

# Management interface using STATIC IP (instead of DHCP)
auto eth0
iface eth0 inet static
  address 192.168.1.14
  gateway 192.168.1.1
  netmask 255.255.255.0
  network 192.168.1.0
  broadcast 192.168.1.255
  # If running Security Onion 14.04, you'll need to configure DNS here
  dns-nameservers 192.168.1.1 192.168.1.2

# AND one or more of the following

# Connected to TAP or SPAN port for traffic monitoring
auto eth1
iface eth1 inet manual
  up ifconfig $IFACE -arp up
  up ip link set $IFACE promisc on
  down ip link set $IFACE promisc off
  down ifconfig $IFACE down
  post-up for i in rx tx sg tso ufo gso gro lro; do ethtool -K $IFACE $i off; done
  # If running Security Onion 14.04, you should also disable IPv6 as follows:
  post-up echo 1 > /proc/sys/net/ipv6/conf/$IFACE/disable_ipv6

You may also want to set the RX buffer size in the post-up command like this:

post-up ethtool -G $IFACE rx 4096; for i in rx tx sg tso ufo gso gro lro; do ethtool -K $IFACE $i off; done

Note that 4096 is just an example and your NIC may have a different maximum rx size. To determine the maximum rx setting for your NIC:

ethtool -g ethX

Restart networking:

sudo /etc/init.d/networking restart

If you already had sensors running on these interfaces, you should restart them:

sudo so-sensor-restart

For more information on network configuration in Ubuntu, please see https://help.ubuntu.com/community/NetworkConfigurationCommandLine/Automatic.