NFV is the abstraction of the physical network to support the running of multiple network logical instances on a common, shared, and physical element. Network instances that are virtualized essentially function similarly to the equivalent physical instance.
A prominent example of network virtualization is VLAN. A VLAN is an abstraction of a physical switch in simple terms; it splits a single L2 broadcast domain into smaller logical domains that coexist without intercommunication between them. Communication between such domains requires the implementation of a layer three switch or a router.
Earlier implementations of network virtualization supported layer two (switching) and layer three (routing) services, but layer four to layer seven services such as firewalls and load balancers are now fully supported by network visualization.
Network virtualization maximizes the physical resources and ultimately grants full control, security, and efficiency to the network administration. It also cuts down the high cost of physical elements when compared to the virtual instances. The operational cost of elements such as cooling, power, and special requirements are cut down.
NFV is often mixed up with SDN. SDN is an approach introduced to bring intelligence into the network, while NFV is used to migrate network appliances such as IDS, VPN, and load balancers from the physical hardware to a virtualized platform.
NFV technologies help cut down cost relatively but without an intelligent approach introduced to manage the virtualized resources. The overall operational cost remains the same because it suffers major constraints that physical hardware deployments suffer, such as manual management of policies.
SDN introduces automation in network infrastructures such that the virtualized services created by NFV can be more methodical and optimized for the maximum utilization of resources. The preceding diagram shows a pictorial view of SDN and NFV combined in a network.
NFV can exist fully without SDN, but SDN is the boost needed to reap the maximum benefit from NFV technology. Even though both technologies differ, combining them allows reduced capital and operational cost as well as optimized traffic flow across the network.
NFV comes with some challenges that require considerations before implementing in existing networks. In large-scale networks, redundancy is a vital characteristic that is essential in order to minimize the downtime of the network if any network element goes down.
With NFV, the deployment should have redundancy at the physical level as well as the virtualized level. For instance, if the redundant switch is hosted on the same physical infrastructure, in the case of a power outage, both switches will fail, leading to a loss of connectivity.
Physical resources required to support a fully virtualized environment are limited. A physical host that supports multiple switch instances will require a network interface card of up to 100 Gbps for optimum functionality. The cost of such hardware to support a fully virtualized environment is on the high side.