Overlay networking enables to implement tunnels to interconnect networks defined inside a host (such as Docker/Podman private networks): for example flannel based Kubernetes uses VxLANs to interconnect the Minion’s private networks. Anyway VxLAN is only one of the available technologies: other technologies such as GENEVE, STT or NVGRE are available.

In this post we setup a GENEVE tunnel with OpenVSwitch and Podman - the described set up goes beyond the simple interconnection on of layer 3 network segments, interconnecting two Podman’s private networks configured with the same IP subnet (so they share the same broadcast domain) - the layer 2 data are exchange between the OpenVSwitch bridges on the two hosts through the GENEVE tunnel.

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OpenVSwitch (OVS) is the pillar used by several emblazoned software, such as OpenStack or Red Hat's OpenShift to set up their Software Defined Networks (SDN): it enables users to quickly and easily implement multiple bridges to which connect Virtual Machines or Containers.

These bridges can be left standalone, creating isolated networks, or interconnected to the machine (or VM) NICs, providing bidirectional access to the network segment the NIC is connected to. In addition to that, it also enables the set up VxLAN Tunnel EndPoint (VTEP) on these bridges, enabling interconnecting OVS bridges from different machines. Last but not least, it also enforces traffic policies defined using OpenFlow.

The SDN tutorial - OpenFlow with OpenVSwitch on Oracle Linux, starts from where we left in the "Free Range Routing (FRR) And OpenVSwitch On OracleLinux" post, extending its Lab and provides a practical guide on how to write and set OpenFlow rules on OpenVSwitch.

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In an Infrastructure As Code (IaC) scenario, rather than provision a VM and install a networking dedicated appliance, it is best to provide something without a web-UI but that provides a good configuration API or that sources its settings from something that can be easily managed by automated configuration tools.

In such as scenario it is more convenient to just use one (or more) Linux VM with a very basic installation, having it manage infrastructural networking: these VM can not only manage networking using routing protocol such as RIP, OCSP and even BGP, but also enforce security policies dropping unauthorised traffic.

In this post we see Free Range Routing (FRR) and OpenVSwitch on Oracle Linux in action, setting up a Lab with two virtual machines providing routing sharing routing tables using OCSP: we achieve this by installing Free Range Routing (FRR) - a free and open source Internet routing protocol suite for Linux. The advanced setup shown in this lab also makes use of OpenVSwitch, stacking FRR on top of it.

This dual layer setup enables us to exploit the Software Defined Networking (SDN) features provided by OpenVSwitch, enhancing by adding dynamic routing support, but also providing a compatibility layer with legacy bare metal devices such as "traditional" hardware routers.

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