Oracle Linux - IPv4 forwarding is disabled. Networking will not work

Using Docker for the first time can be confusing, especially on the networking part. When you run Docker for the first time on a vanilla Oracle Linux instance you might be hitting a networking issue the first time you start a container and try to do network forwarding. By default IPv4 forwarding is disabled and should be set to enabled to make use of Docker in the right way.

The below error might be what you are facing when starting your first docker container on Oracle Linux:

WARNING: IPv4 forwarding is disabled. Networking will not work.

To resolve this issue you will to make changes to the configuration of your Docker host OS. In our case we run a Oracle Linux operating system with the Docker engine on top of it. To ensure you have forwarding active you will have to change setting in /etc/sysctl.conf . By default you will have the following:

# Controls IP packet forwarding
net.ipv4.ip_forward = 0

You will have to change this into 1 as shown below

# Controls IP packet forwarding
net.ipv4.ip_forward = 1 

As soon as you have ensured the new settings are active, and only after you made sure they are active, your Docker containers should start without any issue.