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 Networking in NFV ?

I am often asked whether one needs SDN for NFV. My usual anwer is it depends on how flexible networking one needs.

As long one needs networking , there is a room for SDN. It depends on the level of abstraction you need in the networking layer. How flexible you need the VNFs to move from one data center to another. Do you expect to have more flexible and mobile Workloads or you can keep it within the same data center.

Do you want to create a Telco Cloud where you spin up the services in one data center or the other, than you need it. You need service chaining or not.

In effect, it all goes back to how flexible networking layer you need 

Touch the NFV and visualize it as a Data Center ( Rather a Telco Data Center)

Now lets turn   where is networking needed in the NFV. For that purpose , we will see where is switching and routing needed in NFV. 

Does SDN has a role to play in NFV. 

The answer is yes, whenever there is networking, there is room to intoduce SDN. In this post we will go through where is networking needed in NFV.

The diagrame below shows three servers in an NFVI setup , where VNFs need to communicate with one another. If the VNFs are in the same server, they can communicate through the virtual switch as shown in the hypervisor. However if they have to go to another server, present in the same rack, it will cross the Access switch, which is also the top of the rack switch. Again there is another faster way whish is using SR-IOV bypassing the virtual swithc and use the physical NIC to do the switching. This is faster and consume much lesser resources than if the virtual switch is used.

The most common implementations of VEBs are software-based vSwitches built into hypervisors. Butvendors can use the PCI Single Root I/O Virtualization (SR-IOV) standard to build hardware-based VEBs in NIC

The brown traffic than crosses both access and aggregation switch in order to go from one rack to another rack. Now 

So you can see that there is a lot of networking involved.

But why wouldnt common technologies work in such kind of situations. We have overlay technologies using layer 2 and layer 3 VPN that can help in the communciation between the servers, and than in order to provide tenannt isolution, layer 2 or layer 3 Overlays can be built like VXLANs, STT etc


What is SDN? 

Software Defined Network has a role to play in NFV. However there seems to be a lot of confusion on how and where to position to the SDN controller, what are the different places where one can place the SDN resource. But before starting , lets start with what is SDN; I will use the ITU-T definition of SDN, 

Ref: ITU-T Y.1330 

According to this definition, SDN is a to 

“SDN relocates the control of network resources to a dedicated network element, namely SDN controller, which provides a means to program, orchestrate, control and manage the network resources through software (i.e., SDN applications)”

ONF has summed it up with very nicely, through the following definition

 “The physical separation of the network control plane from the forwarding plane, and where a control plane controls several devices.” 

The question than becomes where are the SDN resources, SDN controller and the applications in the ETSI NFV Architecture.

The resource layer is where the forwarding plane sits. So here comes the question, what is the difference between the control plane and the forwarding plane.


  • Forwarding Plane is responsible for forwarding the traffic
  • Control Plane is responsible on instructing device on how to process and forward the traffic.

So basically SDN separates forwarding and control plane and in this respect controller is where the control plane runs. and it is logically centralized. It does not run on the equipment itself. This makes the equipment simple and scalable and also the network more programmable.

The Application Plane is responsible for the programmatic control of network resources. The controller expose APIs on the North Bound and the Application plane can control the network behavior using those APIs.

Moving forward we will see how SDN resource, SDN Controller and SDN Application fits in the NFV arena

 Why SDN in NFV 

The question than becomes what is the role of SDN. The 

Location of SDN Controller

First of all lets see the location of the SDN Controller. The SDN Controller can be located in any of the five locations:

  • Part of VIM
  • Part of NFVI
  • As VNF
  • Part of OSS
  • As PNF

The location of SDN Controller is implementation dependent. 

Location of SDN Resource

SDN Resource can be located in any of the following positions as shown

  • Physical Switch or Router
  • Virtual Switch or Router
  • e-switch, software based SDN enabled switch in a server NIC 
  • Switch or Router as VNF

Location of SDN Application

SDN Application sits in any of the following positions

  • As part of PNF
  • As part of VIM
  • As part of VNF
  • As part of EM
  • As part of OSS/BSS

 Example of All components in one diagram 

Here is an example of all components of SDN in one NFV Diagram.

All the different components are now added taking one example for SDN Application, Controller and Resource.

After going through the location of different resources, lets turn to the point on the need for the SDN contoller in NFV.

 Purpose of SDN Controller in NFV 

At this time we bring the discussion of VNF-FG as we discussed in the earlier blog.

VNFs may connect using Network service or they may connect without any Network Service Defined. With the NS, VNFs are bonded togather as shown in below diagram that NS-Mobile RAN is one service which NS Mobile Core is a different service. and each service is composed of multiple VNFs.

Do you really need SDN for connecting these VNFs, the answer is NO. Such VNFs can be statically connected using the networks shown in section 1, that is using any layer 2 or layer 3 technology. However at the same time, SDN controller can be used to connect them.

Remember that for Native Cloud system, there is a lot of networking involved between the work loads, so it is is more of how you want to build up your work load.

Then there are micoservices that need connection. The service graph can be distributed over multiple PoDs, that is the beauty of using SDN, as SDN will give more control and Power for the networking

 Use Case No 1: Use SDN for the same reason that it is used in Data Centers today. 

As the SDN Controller is needed to connect a data center fabric, the same can be used for connecting VNFs. In case of multi tenancy or having multiple data centers where data center independence is required. SDN can be used to connect the Data center fabric.


 Use Case No 2: No need to move workloads , No issue. Use it for the Service Chaining Applications that are needed in NFV 

You do not need to move workloads, then perhaps you need a more dynamic behaviour when you create Network service.

For example , you would like to do service chaining in the Gi-Lan, between the DPI, Service Chaining 

 Use Case 3: Dynamic Service Chaining 

This is an example of having to use it for dynamic service chaining of the VNFs so that the traffic can pass through certain network element based on certain network load

 Use Case 4: Load balancing between the Networks 

This could be an interesting use case. As this can be used for the purpose of distributing the network load among two different networks depending on the load conditions

 Use Case: Network Slicing 

The network slicing needs to be explained

 SDN Across Multiple VIMs 

There are two different scenarios

  1. SDN Across multiple VIMs in a single NFVI Data Center
  2. SDN Across multiple VIMs in different NFVI Data Center

SDN Acroos Multiple VIMs in a single NFVI Data Center is handled in a same way . An overlay tunnel is established across multiple VIMs in order to