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Network abstraction and virtualization are similar, but they do have significant differences, as well. All network virtualization is abstracted, but not all network abstraction qualifies as network virtualization. Abstraction is a lower-level concept, while virtualization is a higher-level concept.
With traditional network devices, the data flow is specifically limited to physical paths. For a packet to go from point A to point B, for example, the devices must all have a direct physical connection. Changing configurations ultimately means physically moving cables or devices. This is where abstraction comes in.
Network abstraction breaks physical relationships, which allows virtual routes and devices to be built and offers more networking flexibility. Abstraction enables the creation of virtual network constructs, like a virtual LAN (VLAN), as opposed to a physical route between two destinations, which is a hardware function only.
Basic networking functions, like VLANs and virtual routing and forwarding, provide some level of abstraction today and can be created simply, without all of the complicated overlays involved in true network virtualization.
Explaining network virtualization
In contrast, when people speak of network virtualization, they are typically referring to a more complex concept. Network virtualization combines hardware and software to create a completely software-defined network. Along with virtualizing the network resources, network virtualization also virtualizes the devices. This means physical switches become virtual switches, which exist as software-driven entities and not physical boxes with ports.
Network virtualization is most often seen in highly virtualized compute platforms, like VMware NSX; cloud installations, like OpenStack; or within container confines, like Kubernetes.
Network virtualization can be broken down even further into internal and external virtualization. Internal network virtualization happens at the server level, while external network virtualization happens at the data center level.
With internal network virtualization, all of the network constructs are purely virtual and live within a single system. Running VMware or Xen hypervisor on a single server and enabling connectivity between the different virtual machines on the server is an example of internal network virtualization.
However, when this configuration begins to include external -- physical -- network devices or additional external servers, then it would be referred to as external network virtualization.
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