Open Virtual Network (OVN) is an open source project originally launched by the Open vSwitch (OVS) team at Nicira (now part of VMware) that is supported by engineers from various commercial, private, and public entities. The objective is to develop a single, standard, vendor-neutral protocol for the virtualization of network switching functions, still based on the functionality first created for VMware virtual networks.
Using an open approach to virtual switching, any kind of workload virtualization platform – such as a hypervisor or container platform (e.g., Docker) – may reliably invoke networking functions using the same API. This not only improves scalability but enables easier live migration of virtual network components without hypervisor intervention.
OVN and Network Control
OVN’s main goal is to provide Layers 2 and 3 networking, which distinguishes it from general-purpose, software-defined networking (SDN) protocols and controllers.
Proponents say that OVN enables users to control cloud network resources. You can use OVN to connect VMs or containers into private L2 and L3 networks quickly and programmatically without provisioning VLANs or other physical network resources. OVN includes logical switches and routers, security groups, and L2/L3/L4 ACLs. It is implemented using a tunnel-based overlay network with protocols such as VXLAN, NVGRE, Geneve, STT, and IPsec.
OVN and OpenFlow
OVN can be used with the OpenFlow protocol, which was created as a way of exploiting the capability to manipulate flow tables. Networks employ these to implement network services, such as quality-of-service (QoS) monitors, firewalls, and network address translation (NAT). Historically, vendors have taken advantage of their ability to manipulate these tables in their own unique ways. OpenFlow produces its own system of flow tables, by way of a virtualized set of standard functions supported by routers and switches. This way, a virtual flow controller may dynamically rewrite the map of the network at any time, to implement new instances of network functions as needed, or to remove redundant instances.
By supporting protocols including OpenFlow and OVSDB, OVN can be used to stitch together feature-rich SDNs. OVSDB is instrumental in VMware’s NSX offering for network virtualization – and VMware is the host of the OVS project. OVN takes advantage of OpenFlow extensions that were written for OVS.
OVN and OpenStack Integration
OVN can also be used in OpenStack-based networks, where Open vSwitch is the most popular virtual-switch option. OVN developers are hoping their standard becomes accepted as the default network control plane for OpenStack, the open source hybrid cloud operations platform. (When the team’s documents refer to a “CMS,” or “cloud management system,” it intends to be able to substitute this with “OpenStack.”) The network facilitator in OpenStack is called Neutron, and its default control plane uses OVS.
A transition to OVN, its proponents argue, would be natural and seamless, and would result in highly accelerated scalability, enabling a cloud cluster to become more flexible and mutable, and for its resources to be reconfigured as necessary without downtime. Preferably, the OVS Team would accomplish OpenStack integration by way of a plug-in built in collaboration with OpenStack engineers.
The OVS team says it believes this can be accomplished without compromising the accomplishments of Open vSwitch – that is, by promoting OVN as an implementation of OVS, with the necessary interfaces for virtual applications environments to provision a complete virtual network.