Network Virtualization vs SDN

SDN (Software Defined Networking) and Network Virtualization, although often in the "same basket", are two different concepts.

Network Virtualization (NV) decouples and isolates "virtual" networks from the underlying physical network hardware. SDN is a concept of separating the Data plane from the Control plane. It does look similar. The NV analogy can be made with the Server Virtualization, which has been the most frequently deployed solution in the Data Centres for quite some time now. In my opinion probably the most important term related to NV is the concept of PROVISIONING. What could this mean in Networking terms? Well, like in the example of Virtual Servers, for example VM machines on the ESXi server, it's the ESXi that provisions the physical resources of the Physical Server or a Cluster to accommodate the needs of the VM. In the same manner, Network needs to provision the VLANs, required Firewall rules, and adjust the IP routing to "welcome" the new Application. Basically the aim of NV is to solve the Virtualization gap between networking, compute and storage.

Main Concept here is the the NFV, as a natural complement to SDN Architectures. vRouter is a foundation of NVF: You take the routing and implement it as a Virtual Machine called vRouter and put inside the Server (x86 platform), and also implement some of the security, so you get a VM which is a vRouter containing NFVs such as VPN, Firewall and Router.

A very important VLAN-analog concept appears when we're talking about the Network Virtualization of the Data Center, and as you probably assumed - it's a VXLAN (Virtual Extensible LAN). This technology appears to be a direct response to the multi-tenancy requirements, and the resourse separation between the traffic flows of each of the tennants. Don't be afraid of it, and it will be your friend. VXLAN is an overlay protocol, and it's got an encapsulation and decapsulation process. It's basically like a wrap protocol around an Ethernet frame, nothing more then that. It basically adds 50 bytes of overhead when encapsulating the Ethernet Frame in UDP, so instead of 4096 VLANs - we have 16 million segment IDs. Please check out the below video made by Cisco (don´t you just love this guy?) about the VXLAN fundamentals.

Another inevitable concept is the API. APIs allow software developers to write code that provisions the network as an entire entity. Some of these APIs are public, so the big Networking players, such as Cisco, will publish their APIs and provide a detailed documentation about how to integrate with their products. The list of most popular APIs related to SDN can be found here.

The concepts of VXLAN and APIs are so important that I will definitely dedicate a separate post to each of these.

The problem with the SDN is that everyone seems to have their own way of understanding it. Yes, it's related to the concept of Network Virtualization, but it seems to be more "adjustable" to what the company is trying to sell you. You will see "SDN ready" on many products, and recently I've even found a post on Network World that MRV added a special port called ""the SDN port". Just don't let all this confuse you, and form your own definition of SDN (read more here). One thing is for sure - no metter how you define it now, technology changes so fast in this field that in a few months your definition will be utterly different.


  1. I will go for the SDN the reason is quite simple that Administrative efficiency, improvements in server utilization, better control of visualization, and other benefits should result in operational savings. Although it is still early to show real proof of savings, SDN should lower overall operating costs and result in administrative savings since many of the routine network administration issues can be centralized and automated.

  2. True, lets just wait and see which SDN solution will predominate... talking about the SDN now is like talking about the Cloud 5 years ago, everyone understends it in their own special way

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