1. Brief Introduction to NSX

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NSX is the next evolution of what used to be known as vCloud Networking and Security suite within the VMware’s vCloud suite – A.K.A vCNS (now discontinued) which in tern, was an evolution of the Nicira business VMware acquired a while back. NSX is how VMware provides the SDN (Software Defined networking) capability to the Software Defined Data Center (SDDC). However some may argue that NSX primarily provide a NFV (Network Function Virtualisation) function which is slightly different to that of SDN.

The current version of NSX available comes in 2 forms

  1. NSX-V : NSX for vSphere – This is the most popular version of NSX and is what appears to be the future of NSX. NSX-V is inteneded to be used by all existing and future vSphere users alongside their vSphere (vCenter and ESXi) environment. All the contents of the rest of this post and all my future posts within this blog are referring to this version of NSX and NOT the multi hypervisor version.
  2. NSX-MH : NSX for multi hypervisors is a special version of NSX that is compatible with other hypervisors outside of just vSphere. Though it suggests multi- hypervisors in the name, actual support (as of the time of writing) is limited and is primarily aimed at offering networking and security to OpenStack (Linux KVM) rather than all other hypervisors (currently supported hypervisors are XEN, KVM & ESXi). Also, the rumour is that VMware are phasing NSX-MH out anyway which means all if not most future development and integration efforts would likely be focused around NSX-V. However if you are interested in NSX-MH, refer to the NSX-MH design guide (based on the version 4.2 at the time of  writing) which seems pretty good.

Given below is a high level overview of the architectural differences between the 2 offerings.

1. Differnces between V & MH


NSX-V, or as commonly referred to as NSX, provide a number of features to a typical vSphere based datacentre

2. NSX features

NSX doesn’t do any physical packet forwarding and as such, doesn’t add anything to the physical switching environment. It only exist in the ESXi environment and independent (theoretically speaking) of the underlying network hardware. (Note that NSX however is reliant on a properly designed network in a spine and leaf architecture and require support for MTU > 1600 within the underlying physical network).

  • NSX virtualises Logical Switching:- This is a key feature that enables the creation of a VXLAN overlay network with layer 2 adjacency over an existing, legacy layer 3 IP network. As shown in the diagram below, a layer 2 connectivity between 2 VM’s on the same host never leaves the hypervisor and the end to end communication all takes place in the silicon.  Communication between VM’s in different hosts still has to traverse the underlying network fabric however, compared to before (without NSX), the packet switching is now done within the NSX switch (known as the Logical switch). This logical switch is a dvPort group type of construct added to an existing VMware distributed vSwitch during the installation of NSX

3. Logical Switching

  • NSX virtualises logical routing:- NSX provides the capability to deploy a logical router which can route traffic between different layer 3 subnets without having to physical be routed using a physical router. The diagram below shows how NSX virtualise the layer 3 connectivity in different IP subnets and logical switches without leaving the hypervisor to use a physical router. Thanks to this, routing between 2 VMs in 2 different layer 3 subnets in the same host would no longer require the traffic to be routed by an external, physical router but instead, routed within the same host using the NSX software router allowing the entire transaction to all occur in the silicon. In the past, a VM1 on a port group tagged with vlan 101 on host A, talking to VM2 on a port group tagged with vlan 102 on the same host would have required the packet to be routed using an external router (or a switch with Layer 3 license) that both uplinks / vlans connects to. With NSX, this is no longer required and all routing, weather VM to VM communication in the same host or between different hosts will all be routed using the software router.

4. Logical Routing


  • NSX REST API:-  The built in REST API provide the programmatically access to NSX by external orchestration systems such as VMware vRealize Automation (vCAC). This programmatically access provide the ability to automate the deployment of networking configurations, that can now be tied to application configurations, all being deployed automatically on to the datacentre.

5. Programmatical access

  • NSX Logical Firewall:-  The NSX logical firewall introduces a brand new concept of micro segmentation where, put simply, through the use of a ESXi kernel module driver, un-permitted traffic are blocked at the VM’s vmnic driver level so that the packets are never released in to the virtual network. No other SDN / NFV solution in the market as of now is able to provide this level of micro segmentation (though Cisco ACI is rumoured to bring this capability to ACI platform through the use of the Appliance Virtual Switch).  The NSX logical firewall provide the East-West traffic filtering through the distributed firewall while North-South filtering is provide through the NSX Edge services gateway. The Distributed firewall also allows the capability to integrate with advanced 3rd party layer 4-7 firewalls such as Palo-Alto network firewalls.

6. Firewalls

There are many other benefits of NSX all of which cannot be discussed within the scope of this article. However the above should provide you with a  reasonable insight in to some of the most notable and most discussed benefits of NSX.

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