The Magic of SDN: How Cloud Virtual Networks Work Behind the Scenes

When I started exploring cloud networking, one question caught my attention: how do two virtual machines communicate when they are running on different physical machines, without being directly connected through physical cables? How can cloud platforms create isolated networks, manage IP addresses, and control traffic without requiring a separate physical network for every customer?

This talk explores the ideas behind Software-Defined Networking (SDN), with a practical introduction to Open vSwitch (OVS) and Open Virtual Network (OVN).

We will start with the basic problem that traditional networking faces in virtualised environments and understand how SDN approaches it by separating the control plane from the data plane.

From there, we will look at the role of Open vSwitch as a software-based virtual switch and how OVN builds on it to provide logical switches, logical routers, network isolation, and connectivity between virtual machines.

The main part of the session will walk through OVN's architecture, including the Northbound Database, ovn-northd, Southbound Database, ovn-controller, and Open vSwitch. Using a simple example of two simulated virtual machines communicating across different hosts, we will follow how network configuration is translated into actual packet forwarding.

The aim is to make virtual networking easier to understand by connecting the architecture to a real-world cloud networking scenario, rather than treating SDN and OVN as just a collection of unfamiliar terms.

1.       Understand what Software-Defined Networking is and why it is useful in cloud environments.

2.       Understand the difference between a traditional physical switch and a virtual switch such as Open vSwitch.

3.       Learn what OVN provides on top of Open vSwitch.

4.       Understand the purpose of OVN's Northbound and Southbound Databases.

5.       Follow how a packet travels between virtual machines using an OVN-based logical network.

6.       Get familiar with the open-source technologies that make software-defined cloud networking possible.