Tutorials How to configure floating IP on Ubuntu

How to configure floating IP on Ubuntu

Once you get a confirmation from the UpCloud Support that a floating IP has been added, you can find it attached to one of the servers at your UpCloud control panel. However, using the added IP will require some manual setup. Follow the steps below on how to get this done on Ubuntu servers.

Set up static IP addresses

For this example, the server 1 ( and server 2 ( have a common floating IP, netmask and gateway

Firstly, you’ll need to configure the servers at the OS level, so start up your systems and log in.

Check your current network settings with the following command.

ip addr

Commonly the second network interface card (NIC) named eth0 has your public IPv4 address assigned to it, see the example below.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 6e:d7:1b:bf:5a:b0 brd ff:ff:ff:ff:ff:ff
    inet brd scope global eth0
    valid_lft forever preferred_lft forever

In addition to the IP addresses, you will need the default gateway. It can be found with the command underneath.

route -n
Kernel IP routing table
Destination  Gateway       Genmask        Flags  Metric  Ref  Use  Iface        UG     0       0    0    eth0      UG     0       0    0    eth1  U      0       0    0    eth1  U      0       0    0    eth0

Set the address to static on the NIC with your public IPv4, eth0 in this case. You can do this by editing the interfaces configuration file.

sudo nano /etc/network/interfaces

At the settings group that starts with auto eth0, change the dhcp to static and add the address, netmask and gateway as shown in the example below.

auto eth0
iface eth0 inet static

After making the changes, save the file and exit. You will then need to restart the interface to enable the static configuration.

sudo ifdown eth0 && sudo ifup eth0

If you were connected with SSH, the interface restart should be fast enough to not cause you to disconnect. In case you do loose connection and are unable to reconnect, you can always use the web Console at UpCloud control panel under your Server settings to go through the setup again to make sure everything is entered correctly.

Repeat the steps on your other server to configure it with static IP address as well.

Configure the floating IP

To enable the floating IP, add it as an alias to the network interface with your public static IP configured to. On Ubuntu servers, this can be done by adding eth0:1 to the same interfaces file that you edited before.

sudo nano /etc/network/interfaces

Enter the example configuration shown below with your floating IP and netmask.

auto eth0:1
iface eth0:1 inet static

Save the file and exit after these changes.

Repeat the process to add the alias on any other servers you wish to use the floating IP on.

Enabling traffic to the floating IP

With the new alias interfaces set up, check which server the floating IP is attached to under the Public network list at your UpCloud control panel. You should then turn on the alias NIC on that server, in this case using the following command on your Ubuntu host.

sudo ifup eth0:1

Check your network configuration again with the same command as before.

ip addr

The newly added alias shows up under the NIC with your public IP and the floating IP.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 6e:d7:1b:bf:30:50 brd ff:ff:ff:ff:ff:ff
    inet brd scope global eth0
    valid_lft forever preferred_lft forever
    inet brd scope global secondary eth0:1
    valid_lft forever preferred_lft forever

Now attempt to connect to your server through the floating IP with SSH or if you have a web server configured open the floating IP on your web browser.

If you get a reply, the floating IP works on that server and you can continue forward. If it didn’t work, make sure you entered the IP address and netmask correctly, that your firewall isn’t blocking your connections, or try another method to connect.

Test the configuration

Your configuration should now be complete, you can test that it works by transferring the floating IP from one server to another.

To do this, turn off the floating IP alias NIC on the server it’s currently attached to by using the following command.

sudo ifdown eth0:1

Then turn on the alias NIC on your other server.

sudo ifup eth0:1

Lastly, update the gateway on the new floating IP destination server with arping -S <floating IP> <gateway IP>. In this example, the command would be the following.

sudo arping -S

Test the floating IP again with any method you prefer. When you get a connection you have successfully transferred the floating IP.

Using your new floating IP

You can now transfer the floating IP between your cloud servers by turning off the alias NIC on the current server, and then turning on the alias on the new destination host.

Depending on your intended use case for the floating IP you may wish to continue by setting up automated load balancing, but if you wish to manually transfer the traffic between your servers, it might be useful to create scripts of the required commands.

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