If you want to isolate multiple networks, you can use VLAN (Virtual LAN). On most of the switches, you can configure VLAN to handle tagged packets and be able to send them to a specific port by isolating it. A VLAN is assigned a specific id that can be any number between 1 and 4096.
Most of the Linux distributions can handle tagged packets and VLAN usage, but this feature is not mandatory enabled by default. For the example, I’ll present here how you can enable and configure VLAN on Ubuntu Server 14.04.
First, you need to install the vlan package:
apt-get install vlan
Temporary configuration
Then, you should load the 8021q module into the kernel (guessing you’re using a recent and not customized kernel):
modprobe 8021q
As it’s not possible to create a VLAN on virtual interface, you will have to use physical interface and alias to make it work. You can create additional interface with:
vconfig add eth0 100
Then, you can assign an address to this interface:
ip addr add 172.30.0.1/24 dev eth0.100
And finally make the interface up:
ip link set up eth0.100
Permanent configuration
You have to load the module automatically and permanently:
echo "8021q" >> /etc/modules
Finally, set the configuration in /etc/network/interfaces in order to make it loaded on startup:
auto eth0.100
iface eth0.100 inet static
address 172.30.0.1
netmask 255.255.255.0
network 172.30.0.0
broadcast 172.30.0.255
vlan-raw-device eth0