The Theory of Docker Overlay Networking

Now that you’ve seen how easy it is to build and use a secure overlay network, let’s find out how it’s all put together behind the scenes.

Some of the details will be specific to Linux. However, the same overall principles apply to Windows.

VXLAN primer

First and foremost, Docker overlay networking uses VXLAN tunnels to create virtual Layer 2 overlay networks. So, before we go any further, let’s do a quick VXLAN primer.

At the highest level, VXLANs let you create a virtual Layer 2 network on top of an existing Layer 3 infrastructure. That’s a lot of techno-jargon that means you can create a simple network that hides horrifically complex networks beneath. The example we used earlier created a new 10.0.0.0/24 Layer 2 network on top of a Layer 3 IP network comprising two Layer 2 networks; 172.31.1.0/24 and 192.168.1.0/24.