Floating IP is a public accessible IP address that can be assigned to a dedicated server and then reassigned to another dedicated server as needed. It can be used to send outbound traffic or to implement a fail over mechanism. In this case, you are going to approach the outbound traffic use case.
By default, when you assign a Floating IP to a dedicated server, the traffic originating from the server to the Internet does not use the floating IP as source address.
In Linux, your default gateway always uses the first IP address of the public network interface.
So this guide describes how you can (re)configure your operating system to use the Floating IP as the source address for outbound traffic in three different operating systems:
To check which IP is used as the source for outbound traffic, you can use a service like ifconfig.co
$ curl -4 ifconfig.co
212.32.230.67
In this example, 212.32.230.67 is the public IP of the dedicated server.
CentOS 7
Check the current Outbound IP
By running the following command you are able to get the current Outbound IP of your dedicated server:
# curl -4 https://ifconfig.co/
212.32.230.67
Where 212.32.230.67 is the public IP of the dedicated server.
Add the Floating IP to the machine
Check which interface of the dedicated server has the Public IP by running the following command:
# ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp2s0: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 28:92:4a:33:48:e6 brd ff:ff:ff:ff:ff:ff
inet 212.32.230.67/26 brd 212.32.230.127 scope global enp2s0
valid_lft forever preferred_lft forever
inet6 fe80::2a92:4aff:fe33:48e6/64 scope link
valid_lft forever preferred_lft forever
3: eno1: mtu 9000 qdisc pfifo_fast state UP group default qlen 1000
link/ether 28:92:4a:33:48:e7 brd ff:ff:ff:ff:ff:ff
inet 10.32.18.210/27 brd 10.32.18.223 scope global dynamic eno1
valid_lft 12307sec preferred_lft 12307sec
inet6 fe80::2a92:4aff:fe33:48e7/64 scope link
valid_lft forever preferred_lft forever
You can see that the Public IP 212.32.230.67 of the dedicated server is in the interface enp2s0. So you need to edit the interface by running the following command:
# vi /etc/sysconfig/network-scripts/ifcfg-enp2s0
Ensure the content is like this:
DEVICE=enp2s0
BOOTPROTO=none
ONBOOT=yes
PREFIX=26
IPADDR=212.32.230.67
#GATEWAY=212.32.230.126
DOMAIN=dedi.leaseweb.net
DNS1=23.19.53.53
DNS2=23.19.52.52
#DEFROUTE=yes
You then need to add the Floating IP to the interface by creating the ifcfg-enp2s0:1 file via:
# vi /etc/sysconfig/network-scripts/ifcfg-enp2s0:1
with the following content:
BOOTPROTO=static
DEVICE=enp2s0:1
IPADDR=
PREFIX=32
TYPE=Ethernet
USERCTL=no
ONBOOT=yes
Don’t forget to replace E.F.G.H.
After that we need to add the route to use the Floating IP instead of the Public IP of the dedicated server by creating the following file via:
# vi /etc/sysconfig/network-scripts/route-enp2s0
with the following content:
default via dev enp2s0 src
Don’t forget to replace GATEWAY value that was commented in the first edited file and
So the last step is to apply the configuration that we have changed by running the following command:
# systemctl restart network
Note: Please keep in mind that it would take some seconds before the connection gets established again.
Check if the IP was added to the interface successfully
# ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp2s0: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 28:92:4a:33:48:e6 brd ff:ff:ff:ff:ff:ff
inet 212.32.230.67/26 brd 212.32.230.127 scope global enp2s0
valid_lft forever preferred_lft forever
inet /32 brd scope global enp2s0:1
valid_lft forever preferred_lft forever
inet6 fe80::2a92:4aff:fe33:48e6/64 scope link
valid_lft forever preferred_lft forever
3: eno1: mtu 9000 qdisc pfifo_fast state UP group default qlen 1000
link/ether 28:92:4a:33:48:e7 brd ff:ff:ff:ff:ff:ff
inet 10.32.18.210/27 brd 10.32.18.223 scope global dynamic eno1
valid_lft 84397sec preferred_lft 84397sec
inet6 fe80::2a92:4aff:fe33:48e7/64 scope link
valid_lft forever preferred_lft forever
In the example above, the eno0 where our public IP of the machine 212.32.230.67 is already assigned to.
Check if the Floating IP is the new Outbound IP
By running the following command, you should see the Floating IP instead of the Public IP of the dedicated server:
# curl -4 https://ifconfig.co/
Where Debian 12
Check the current Outbound IP
By running the following command, you are able to get the current Outbound IP of your dedicated server:
# curl -4 https://ifconfig.co/
212.32.230.67
Where 212.32.230.67 is the public IP of the dedicated server.
Add the Floating IP to the machine
Check which interface of the dedicated server has the Public IP by running the following command:
# ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno0: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e6 brd ff:ff:ff:ff:ff:ff
altname enp2s0
inet 212.32.230.67/26 brd 212.32.230.127 scope global eno0
valid_lft forever preferred_lft forever
inet6 fe80::2a92:4aff:fe33:48e6/64 scope link
valid_lft forever preferred_lft forever
3: eno1: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e7 brd ff:ff:ff:ff:ff:ff
altname enp3s0
inet 10.32.18.210/27 brd 10.32.18.223 scope global dynamic eno1
valid_lft 85332sec preferred_lft 85332sec
inet6 fe80::2a92:4aff:fe33:48e7/64 scope link
valid_lft forever preferred_lft forever
We can see that the Public IP 212.32.230.67 of the dedicated server is in the interface eno0. So you need to edit the interface by adding the following block of code by running the following command:
# vi /etc/network/interfaces
Ensure the content is like this:
```bash
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
source /etc/network/interfaces.d/*
# The loopback network interface
auto lo
iface lo inet loopback
auto eno0
iface eno0 inet static
address 212.32.230.67
netmask 255.255.255.192
network 212.32.230.64
broadcast 212.32.230.127
gateway 212.32.230.126
dns-search dedi.leaseweb.net
dns-nameservers 23.19.53.53 23.19.52.52
auto eno1
iface eno1 inet dhcp
mtu 9000
Add the following block of code after the eno0 interface definition:
auto eno0:1
iface eno0:1 inet static
address
netmask 32
up ip route replace default via dev eno0 src
Don’t forget to replace gateway value that is in the eno0 definition block and
So the last step is to apply the configuration that we have changed by running the following command:
# systemctl restart networking
Note: Please keep in mind that it would take some seconds before the connection gets established again.
Check if the IP was added to the interface successfully
# ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno0: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e6 brd ff:ff:ff:ff:ff:ff
altname enp2s0
inet 212.32.230.67/26 brd 212.32.230.127 scope global eno0
valid_lft forever preferred_lft forever
inet /32 scope global eno0:1
valid_lft forever preferred_lft forever
inet6 fe80::2a92:4aff:fe33:48e6/64 scope link
valid_lft forever preferred_lft forever
3: eno1: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e7 brd ff:ff:ff:ff:ff:ff
altname enp3s0
inet 10.32.18.210/27 brd 10.32.18.223 scope global dynamic eno1
valid_lft 86395sec preferred_lft 86395sec
inet6 fe80::2a92:4aff:fe33:48e7/64 scope link
valid_lft forever preferred_lft forever
In the example above, the eno0 where our public IP of the machine 212.32.230.67 is already assigned to.
Check if the Floating IP is the new Outbound IP
By running the following command, you should see the Floating IP instead of the Public IP of the dedicated server:
# curl -4 https://ifconfig.co/
Where
Ubuntu 22.04
Check the current Outbound IP
By running the following command, you are able to get the current Outbound IP of your dedicated server:
# curl -4 https://ifconfig.co/
212.32.230.67
Where 212.32.230.67 is the public IP of the dedicated server.
Add the Floating IP to the machine
# vi /etc/netplan/01-netcfg.yaml
With the following content:
---
network:
version: 2
renderer: networkd
ethernets:
eno0:
dhcp4: no
dhcp6: no
addresses:
- A.B.C.D
-
routes:
- to: default
via: 212.32.230.126
from:
metric: 100
on-link: true
nameservers:
search: [dedi.leaseweb.net]
addresses: [23.19.53.53, 23.19.52.52]
eno1:
dhcp4: yes
mtu: 9000
Do not forget to replace
After that, you need to apply the configuration that you have changed by running the following command:
# netplan applyCheck if the IP was added to the interface successfully
# ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno0: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e6 brd ff:ff:ff:ff:ff:ff
altname enp2s0
inet A.B.C.D/26 brd 212.32.230.127 scope global eno0
valid_lft forever preferred_lft forever
inet scope global eno0
valid_lft forever preferred_lft forever
inet6 fe80::2a92:4aff:fe33:48e6/64 scope link
valid_lft forever preferred_lft forever
3: eno1: mtu 9000 qdisc fq_codel state UP group default qlen 1000
link/ether 28:92:4a:33:48:e7 brd ff:ff:ff:ff:ff:ff
altname enp3s0
inet 10.32.18.210/27 metric 100 brd 10.32.18.223 scope global dynamic eno1
valid_lft 86181sec preferred_lft 86181sec
inet6 fe80::2a92:4aff:fe33:48e7/64 scope link
valid_lft forever preferred_lft forever
In the example above, the eno0 where our public IP of the machine A.B.C.D is assigned to.
Check if the Floating IP is the new Outbound IP
By running the following command, you should see the Floating IP instead of the Public IP of the dedicated server:
# curl -4 https://ifconfig.co/
Where
