How is network virtualization useful?

Question

I am trying to understand various virtualization techniques, and I am struggling to wrap my head around the concept of Network Virtualization.

In case of the server virtualization, the objective is the most efficient use of hardware(using hypervisor), and the alternative is the under utilization of resources. Does that apply in case of network virtualization as well? Is it possible for routers/switches to be under-utilized like a computer's CPU?

Server virtualization uses hypervisor(like virtual box) in spinning up virtual machines. Does network virtualization also make use of hypervisors on top of networking hardware like routers/switches? I have done some research online, but it is not clear to me how hypervisor might factor in network virtualization,

Can somebody give me a high level idea of how network virtualization is implemented, and what benefits it gives.

Answer 1

Network virtualization is a prerequisite for OS virtualization. Imagine, you would have to pull a separate physical network cable for every VM! Imagine you would have to physically re-wire your network every time a VM gets migrated from one node in your hypervisor cluster to another!

If you want to abstract computation from the physical hardware, you also need to abstract networking – after all, typically, the compute process needs to talk to other services to perform its task..

Answer 2

the objective is the most efficient use of hardware(using hypervisor), and the alternative is the under utilization of resources

Not necessarily: the objective may be the easier management of systems, and one key thing you can do with network virtualization is reconfigure your network without having to send technicians to carefully plug and unplug thousands of network cables.

Arguably this is a big part of why AWS is a $90bn business. You never have to move hardware around, an entire business can be reconfigured from the admin console.

Answer 3

If you create a cluster of computers in the cloud, the cluster gets its own internal network between the nodes. If all the nodes in the virtual cluster are on separate physical nodes, this would be implemented as an isolated VLAN on real hardware switches.

If, however, these nodes were actually VMs all or some of which were on the same node, you would use a virtualized network switch that routes data between the VMs without ever touching a real switch... unless it has to leave the node.

Then you add software defined networking which bridges the gap between the virtualized network between VMs on the same hardware, and dynamically created VLANs that extend that virtualized network to other physical nodes to reach VMs on those nodes.

From the VM's perspective, there is no difference between the virtualized network and the actual VLANs on real hardware.

The alternative to this is that each VM has to have a dedicated hardware network interface (this is available on some hardware) that goes to a real switch, and multiple customer's machines all end up on the same physical network, possibly mixing traffic and talking to each other, which might be undesirable.

The virtualized network provides both dynamic reconfiguration, isolation, and emulation of virtualized hardware, reducing actual hardware.