We started our blog series on software defined networking (SDN) use cases by looking at how SDN might enable network virtualization (http://communities.intel.com/community/wired/blog/2013/03/01/sdn-use-cases-network-virtualization).  We continue on a somewhat similar application by looking at SDN and virtual network appliances. 


Many networks utilize specialized appliances, such as firewalls, load balancers, WAN accelerators and others, to provide specialized network packet processing and functionality.


Many of these are now being turned into virtual appliances.  The term “virtual appliance” was coined to describe a self-contained virtual machine powered by an operating system that had a pre-configured application on top.


In the enterprise data center, one of the challenges of the virtual network appliance is that it often needs to be in the data path – either before the router, in the case of a firewall, or before a server, in the case of a load balancer. 


SDN replaces IP routing functionality on each switch with a network controller that can see all data and resources on the network and directs data flows.  With this global view, it can redirect data packets to virtual network appliances directly. In essence, it creates a data path for each data flow in order to direct it to the right virtual appliance.


This is also important in cloud applications where multi-tenant virtual servers may need dramatically different resources and where virtual data paths complicate the sharing of virtual appliances.


The network flow flexibility that SDN brings to datacenter and cloud networks makes virtual network appliances an even more viable and cost-effective way to deliver the network processing needed for secure and high-performance networks.