VMware NSX Overview

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 What is VMware NSX?

VMware NSX is a virtual networking and security software product family created from VMware’s vCloud Networking and Security (vCNS) and Nicira Network Virtualization Platform (NVP) intellectual property.


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IT organizations have gained significant benefits as a direct result of server virtualization. Server consolidation reduced physical complexity, increased operational efficiency and the ability to dynamically re-purpose underlying resources to quickly and optimally meet the needs of increasingly dynamic business applications.

VMware’s Software Defined Data Center (SDDC) architecture is now extending virtualization technologies across the entire physical data center infrastructure. VMware NSX®, the network virtualization platform, is a key product in the SDDC architecture.

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With NSX, virtualization delivers for networking what it has already delivered for compute and storage. In much the same way that server virtualization programmatically creates, snapshots, deletes and restores software-based virtual machines (VMs), NSX network virtualization programmatically creates, snapshots, deletes, and restores software-based virtual networks.

The result is a completely transformative approach to networking that not only enables data center managers to achieve orders of magnitude better agility and economics, but also allows for a vastly simplified operational model for the underlying physical network. With the ability to be deployed on any IP network, including both existing traditional networking models and next-generation fabric architectures from any vendor, NSX is a completely non-disruptive solution. In fact, with NSX, the physical network infrastructure you already have is all you need to deploy a software-defined data center

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The figure above draws an analogy between compute and network virtualization. With server virtualization, a software abstraction layer (server hypervisor) reproduces the familiar attributes of an x86 physical server (for example, CPU, RAM, Disk, NIC) in software, allowing them to be programmatically assembled in any arbitrary combination to produce a unique VM in a matter of seconds.

With network virtualization, the functional equivalent of a network hypervisor reproduces the complete set of Layer 2 through Layer 7 networking services (for example, switching, routing, access control, firewalling, QoS, and load balancing) in software. As a result, these services can be programmatically assembled in any arbitrary combination, to produce unique, isolated virtual networks in a matter of seconds.

With network virtualization, benefits similar to server virtualization are derived. For example, just as VMs are independent of the underlying x86 platform and allow IT to treat physical hosts as a pool of compute capacity, virtual networks are independent of the underlying IP network hardware and allow IT to treat the physical network as a pool of transport capacity that can be consumed and repurposed on demand. Unlike legacy architectures, virtual networks can be provisioned, changed, stored, deleted, and restored programmatically without reconfiguring the underlying physical hardware or topology. By matching the capabilities and benefits derived from familiar server and storage virtualization solutions, this transformative approach to networking unleashes the full potential of the software-defined data center.

NSX can be configured through the vSphere Web Client, a command-line interface (CLI), and a REST API.

NSX Components

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The NSX data plane consists of the NSX vSwitch, which is based on the vSphere Distributed Switch (VDS) with additional components to enable services. NSX kernel modules, userspace agents, configuration files, and install scripts are packaged in VIBs and run within the hypervisor kernel to provide services such as distributed routing and logical firewall and to enable VXLAN bridging capabilities.

The NSX vSwitch (vDS-based) abstracts the physical network and provides access-level switching in the hypervisor. It is central to network virtualization because it enables logical networks that are independent of physical constructs, such as VLANs. Some of the benefits of the vSwitch are:

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Support for overlay networking with protocols (such as VXLAN) and centralized network configuration. Overlay networking enables the following capabilities:

Reduced use of VLAN IDs in the physical network.

Creation of a flexible logical Layer 2 (L2) overlay over existing IP networks on existing physical infrastructure without the need to re-architect any of the data center networks

Provision of communication (east–west and north–south), while maintaining isolation between tenants

Application workloads and virtual machines that are agnostic of the overlay network and operate as if they were connected to a physical L2 network

Facilitates massive scale of hypervisors

Multiple features—such as Port Mirroring, NetFlow/IPFIX, Configuration Backup and Restore, Network Health Check, QoS, and LACP—provide a comprehensive toolkit for traffic management, monitoring, and troubleshooting within a virtual network

The logical routers can provide L2 bridging from the logical networking space (VXLAN) to the physical network (VLAN).

The gateway device is typically an NSX Edge virtual appliance. NSX Edge offers L2, L3, perimeter firewall, load balancing, and other services such as SSL VPN and DHCP.

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Control Plane

The NSX control plane runs in the NSX Controller cluster. NSX Controller is an advanced distributed state management system that provides control plane functions for NSX logical switching and routing functions. It is the central control point for all logical switches within a network and maintains information about all hosts, logical switches (VXLANs), and distributed logical routers.

The controller cluster is responsible for managing the distributed switching and routing modules in the hypervisors. The controller does not have any dataplane traffic passing through it. Controller nodes are deployed in a cluster of three members to enable high-availability and scale. Any failure of the controller nodes does not impact any data-plane traffic.

NSX Controllers work by distributing network information to hosts. To achieve a high level of resiliency the NSX Controller is clustered for scale out and HA. NSX Controllers must be deployed in a three-node cluster. The three virtual appliances provide, maintain, and update the state of all network functioning within the NSX domain. NSX Manager is used to deploy NSX Controller nodes.

The three NSX Controller nodes form a control cluster. The controller cluster requires a quorum (also called a majority) in order to avoid a “split-brain scenario.” In a split-brain scenario, data inconsistencies originate from the maintenance of two separate data sets that overlap. The inconsistencies can be caused by failure conditions and data synchronization issues. Having three controller nodes ensures data redundancy in case of failure of one NSX Controller node.

A controller cluster has several roles, including:

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API provider

Persistence server

Switch manager

Logical manager

Directory server

Each role has a master controller node. If a master controller node for a role fails, the cluster elects a new master for that role from the available NSX Controller nodes. The new master NSX Controller node for that role reallocates the lost portions of work among the remaining NSX Controller nodes.

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NSX supports three logical switch control plane modes: multicast, unicast and hybrid. Using a controller cluster to manage VXLAN-based logical switches eliminates the need for multicast support from the physical network infrastructure. You don’t have to provision multicast group IP addresses, and you also don’t need to enable PIM routing or IGMP snooping features on physical switches or routers.

Thus, the unicast and hybrid modes decouple NSX from the physical network. VXLANs in unicast control-plane mode do not require the physical network to support multicast in order to handle the broadcast, unknown unicast, and multicast (BUM) traffic within a logical switch. The unicast mode replicates all the BUM traffic locally on the host and requires no physical network configuration. In the hybrid mode, some of the BUM traffic replication is offloaded to the first hop physical switch to achieve better performance. Hybrid mode requires IGMP snooping on the first-hop switch and access to an IGMP querier in each VTEP subnet.

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The NSX management plane is built by the NSX Manager, the centralized network management component of NSX. It provides the single point of configuration and REST API entry-points.

The NSX Manager is installed as a virtual appliance on any ESX™ host in your vCenter Server environment. NSX Manager and vCenter have a one-to-one relationship. For every instance of NSX Manager, there is one vCenter Server. This is true even in a cross-vCenter NSX environment.

In a cross-vCenter NSX environment, there is both a primary NSX Manager and one or more secondary NSX Managers. The primary NSX Manager allows you to create and manage universal logical switches, universal logical (distributed) routers and universal firewall rules. Secondary NSX Managers are used to manage networking services that are local to that specific NSX Manager. There can be up to seven secondary NSX Managers associated with the primary NSX Manager in a cross-vCenter NSX environment.

The consumption of NSX can be driven directly through the NSX Manager user interface, which is available in the vSphere Web Client. Typically end users tie network virtualization to their cloud management platform for deploying applications. NSX provides rich integration into virtually any CMP through REST APIs. Out-of-the-box integration is also available through VMware vCloud Automation Center, vCloud Director, and OpenStack with the Neutron plug-in for NSX.

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You can install NSX Edge as an edge services gateway (ESG) or as a distributed logical router (DLR). The number of edge appliances including ESGs and DLRs is limited to 250 on a host.

Uplink interfaces of ESGs connect to uplink port groups that have access to a shared corporate network or a service that provides access layer networking. Multiple external IP addresses can be configured for load balancer, site-to-site VPN, and NAT services.

A logical router can have eight uplink interfaces and up to a thousand internal interfaces. An uplink interface on a DLR generally peers with an ESG, with an intervening Layer 2 logical transit switch between the DLR and the ESG. An internal interface on a DLR peers with a virtual machine hosted on an ESX hypervisor with an intervening logical switch between the virtual machine and the DLR.The DLR has two main components:

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The DLR control plane is provided by the DLR virtual appliance (also called a control VM). This VM supports dynamic routing protocols (BGP and OSPF), exchanges routing updates with the next Layer 3 hop device (usually the edge services gateway) and communicates with the NSX Manager and the NSX Controller cluster. High-availability for the DLR virtual appliance is supported through active-standby configuration: a pair of virtual machines functioning in active/standby modes are provided when you create the DLR with HA enabled.

At the data-plane level, there are DLR kernel modules (VIBs) that are installed on the ESXi hosts that are part of the NSX domain. The kernel modules are similar to the line cards in a modular chassis supporting Layer 3 routing. The kernel modules have a routing information base (RIB) (also known as a routing table) that is pushed from the controller cluster. The data plane functions of route lookup and ARP entry lookup are performed by the kernel modules. The kernel modules are equipped with logical interfaces (called LIFs) connecting to the different logical switches and to any VLAN-backed port-groups. Each LIF has assigned an IP address representing the default IP gateway for the logical L2 segment it connects to and a vMAC address. The IP address is unique for each LIF, whereas the same vMAC is assigned to all the defined LIFs.

Logical Routing Components


A DLR instance is created from the NSX Manager UI (or with API calls), and routing is enabled, leveraging either OSPF or BGP.


The NSX Controller leverages the control plane with the ESXi hosts to push the new DLR configuration including LIFs and their associated IP and vMAC addresses.


Assuming a routing protocol is also enabled on the next-hop device (an NSX Edge [ESG] in this example), OSPF or BGP peering is established between the ESG and the DLR control VM. The ESG and the DLR can then exchange routing information:

The DLR control VM can be configured to redistribute into OSPF the IP prefixes for all the connected logical networks ( and in this example). As a consequence, it then pushes those route advertisements to the NSX Edge. Notice that the next hop for those prefixes is not the IP address assigned to the control VM ( but the IP address identifying the data-plane component of the DLR ( The former is called the DLR “protocol address,” whereas the latter is the “forwarding address.”

The NSX Edge pushes to the control VM the prefixes to reach IP networks in the external network. In most scenarios, a single default route is likely to be sent by the NSX Edge, because it represents the single point of exit toward the physical network infrastructure.


The DLR control VM pushes the IP routes learned from the NSX Edge to the controller cluster.


The controller cluster is responsible for distributing routes learned from the DLR control VM to the hypervisors. Each controller node in the cluster takes responsibility of distributing the information for a particular logical router instance. In a deployment where there are multiple logical router instances deployed, the load is distributed across the controller nodes. A separate logical router instance is usually associated with each deployed tenant.


The DLR routing kernel modules on the hosts handle the data-path traffic for communication to the external network by way of the NSX Edge.

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The NSX components work together to provide the following functional services.

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A cloud deployment or a virtual data center has a variety of applications across multiple tenants. These applications and tenants require isolation from each other for security, fault isolation, and non-overlapping IP addresses. NSX allows the creation of multiple logical switches, each of which is a single logical broadcast domain. An application or tenant virtual machine can be logically wired to a logical switch. This allows for flexibility and speed of deployment while still providing all the characteristics of a physical network’s broadcast domains (VLANs) without physical Layer 2 sprawl or spanning tree issues.

A logical switch is distributed and can span across all hosts in vCenter (or across all hosts in a cross-vCenter NSX environment). This allows for virtual machine mobility (vMotion) within the data center without limitations of the physical Layer 2 (VLAN) boundary. The physical infrastructure is not constrained by MAC/FIB table limits, because the logical switch contains the broadcast domain in software.

Routing provides the necessary forwarding information between Layer 2 broadcast domains, thereby allowing you to decrease the size of Layer 2 broadcast domains and improve network efficiency and scale. NSX extends this intelligence to where the workloads reside for East-West routing. This allows more direct VM-to-VM communication without the costly or timely need to extend hops. At the same time, NSX logical routers provide North-South connectivity, thereby enabling tenants to access public networks.

Logical Firewall provides security mechanisms for dynamic virtual data centers. The Distributed Firewall component of Logical Firewall allows you to segment virtual datacenter entities like virtual machines based on VM names and attributes, user identity, vCenter objects like datacenters, and hosts, as well as traditional networking attributes like IP addresses, VLANs, and so on. The Edge Firewall component helps you meet key perimeter security requirements, such as building DMZs based on IP/VLAN constructs, and tenant-to-tenant isolation in multi-tenant virtual data centers.

The Flow Monitoring feature displays network activity between virtual machines at the application protocol level. You can use this information to audit network traffic, define and refine firewall policies, and identify threats to your network.

SSL VPN-Plus allows remote users to access private corporate applications. IPsec VPN offers site-to-site connectivity between an NSX Edge instance and remote sites with NSX or with hardware routers/VPN gateways from 3rd-party vendors. L2 VPN allows you to extend your datacenter by allowing virtual machines to retain network connectivity while retaining the same IP address across geographical boundaries.

The NSX Edge load balancer distributes client connections directed at a single virtual IP address (VIP) across multiple destinations configured as members of a load balancing pool. It distributes incoming service requests evenly among multiple servers in such a way that the load distribution is transparent to users. Load balancing thus helps in achieving optimal resource utilization, maximizing throughput, minimizing response time, and avoiding overload.

Service Composer helps you provision and assign network and security services to applications in a virtual infrastructure. You map these services to a security group, and the services are applied to the virtual machines in the security group using a Security Policy.

Data Security provides visibility into sensitive data stored within your organization’s virtualized and cloud environments and reports any data security violations.

3rd-party solution providers can integrate their solutions with the NSX platform, thus enabling customers to have an integrated experience across VMware products and partner solutions. Data center operators can provision complex, multi-tier virtual networks in seconds, independent of the underlying network topology or components.

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Check out the Vmware NSX Video Series 

VMware NSX 6.2 Document Center

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