In this guide we will show how you can configure networkd to assign multiple IP addresses to one NIC, but also how to configure multiple Gateways in the same configuration.

The setup looks as following:

The device with the one NIC needs to access:

• LAN-1: 192.168.100.1/24 network – no DHCP present
• LAN-2:192.168.50.1/24 network – no DHCP present
• DHCP-LAN:the network from the router with the DHCP

For that, we need to configure one dynamic  IP, coming from the DHCP and two static IPs to access LAN-1 and LAN-2. To configure this setup, we are going to use <a href="https://wiki.archlinux.org/index.php/Systemd-networkd" target="_blank" rel="nofollow noopener noreferrer">systemd-networkd</a>. This guide will assume Ubuntu > 16.04 but similar idea should hold for other distributions.

Step 1: Enable networkd

sudo systemctl unmask systemd-networkd.service &&\
sudo systemctl enable systemd-networkd.service

Step 2: Configure NIC

In case you need to rename your NIC, check this.

Create a new .network file /etc/systemd/network/10-nicx.network:

[Match]
Name=eth0

[Network]
DHCP=ipv4
DNS=8.8.8.8
DNS=8.8.4.4

# LAN_1
[Address]
Label=eth0:0
Address=192.168.100.10/24

# LAN_2 - Has also a Gateway
[Address]
Label=eth0:1
Address=192.168.50.70/24

# "Static"-Gateway as backup
[Route]
Gateway=192.168.50.1
#Destination=0.0.0.0/0
Metric=1025 # The Gateway of the DHCP gets the default 1024

Restart the networkd:

sudo systemctl restart systemd-networkd.service

and you are good to go!

Done – test

Check the routing table with route -n:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    1024   0        0 eth0
0.0.0.0         192.168.50.1    0.0.0.0         UG    1025   0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.1.1     0.0.0.0         255.255.255.255 UH    1024   0        0 eth0
192.168.50.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0

In this case, the 192.168.1.1/24 network is coming from the router with the DHCP.

You also check with ip route get 8.8.8.8 which gateway is being used:

8.8.8.8 via 192.168.1.1 dev eth0 src 192.168.1.189 uid 1000 
    cache

Additional/Optional Steps

Rename NIC

To rename a NIC using networkd we are going to use the <a href="https://wiki.archlinux.org/index.php/Systemd-networkd#link_files" target="_blank" rel="nofollow noopener noreferrer">.link</a> files. Create a new file /etc/systemd/network/10-nicx-rename.link:

[Match]
MACAddress=00:25:90:4b:81:54

[Link]
Name=newname

Once it is renamed, re-generate your initramfs:

update-initramfs -c -k all

Reboot!

Disable udev rules, e.g. for usb-ethernet device

If you NIC is a USB-device, chances are that there are already udev for it. Usually those rules will kick in first before systemdhas the chance to rename the device using the .link file.

So depending on the distro you should look into this. As an example for the latest debian distros and for USB-network devices you can comment all the lines of the /lib/udev/rules.d/73-usb-net-by-mac.rules. Don’t forget to reload the rules:

sudo udevadm control --reload-rules && sudo udevadm trigger

Disable NetworkManager

Normally you should not have issues running NetworkManager in parallel. NetworkManager is being used in the debian distributions to manage connections. Netplan by default uses NetworkManager. In case you are having issues you can disable the NetworkManager and only use networkd.

Disable Network Manager and enable systemd-networkd

sudo systemctl stop NetworkManager && \
sudo systemctl disable NetworkManager && \
sudo systemctl mask NetworkManager && \
sudo systemctl disable NetworkManager-wait-online.service

Next, start and enable the systemd-networkd service:

sudo systemctl unmask systemd-networkd.service && \
sudo systemctl enable systemd-networkd.service && \
sudo systemctl start systemd-networkd.service

If you want you can also update netplan:

# /etc/netplan/<>.yaml
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: yes

Apply the changes by running the following command:

sudo netplan apply

Enable NetworkManager and Disable systemd networkd

First, stop the systemd-networkd service:

sudo systemctl disable systemd-networkd.service && \
sudo systemctl mask systemd-networkd.service && \
sudo systemctl stop systemd-networkd.service

Start the NetworkManager Service:

sudo systemctl unmask NetworkManager && \
sudo systemctl enable NetworkManager && \
sudo systemctl enable NetworkManager-wait-online.service && \
sudo systemctl start NetworkManager && \
sudo systemctl start NetworkManager-wait-online.service

Restore netplan if needed:

# /etc/netplan/<>.yaml
network:
  version: 2
  renderer: NetworkManager

Generate backend specific configuration files for NetworkManager with netplan command:

sudo netplan generate && \
<code class="language-">sudo systemctl restart NetworkManager

Now the NetworkManager is enabled, interface configurations can be done via the GUI or from the command line, using the nmcli command.