Introduction to Network Virtualization


A 5G world has virtualization at its core. As the number of out connected devices mushrooms from the hundreds of millions to the tens of billions, data centers are relying more and more on virtualized infrastructure to handle the tsunami of data that we're producing and consuming. And it's not just data centers: the fact that 100% of the Fortune 100 companies use virtualization (and VMware virtualization technology at that), tells its own story.
In the Software-Defined Data Center (SDDC), computing, networking, and storage infrastructure are virtualized so that resources can be pooled and used more efficiently, less expensively, and faster. Considerable strides have been made in server (compute) virtualization and are increasingly being seen with storage virtualization.
The efficiencies gained from them, however, have been limited to a certain extent by legacy, (i.e, traditional, non-virtual) network infrastructure that's still reliant on physical hardware and mainly manual processes. While an organization's virtualized compute and storage may be dynamic, agile, and flexible, its legacy networking just can't keep up.
An infrastructure or organization that can't keep up often gets left behind.
Network virtualization enables the speed, mobility, and security needed in a 5G world. Infrastructure can be made ready for new applications or be changed in minutes, rather than days or weeks. Apps and workloads are no longer restricted to individual physical subnets, neither are switches, routers, firewalls, etc. The security focus moves from simply protecting the perimeter (the outside surface) of a data center's infrastructure to providing the ability to give each virtual machine and virtual network its own firewall, shifting the focus to the inside perimeter of the data center and reducing the attack surface. In addition, virtual networks are isolated . and (as we will learn later in this course) segmented from each other and from the underlying physical infrastructure so that threats cannot be spread if they do get in.
Network virtualization extends these features and many others to the cloud as well, a critical factor to the 81% of enterprises that now use multiple cloud deployment models.

What is Network Virtualization?

Network virtualization totally separates network resources from physical hardware by recreating those networking resources in software- by virtualizing them. Physical routers (which forwards data across multiple networks,) switches (which forwards data on a single Local Area Network or LAN) and load balancers (which even out workloads to prevent servers from being overwhelmed) are virtualized in the hypervisor layer using off-the-shelf, industry-standard servers (server/compute hosts). This virtualized pool can then be used as needed, on-demand. The underlying physical hardware remains important (it's still used for forwarding) but no longer needs to be reconfigured every time a new VM or container is added or updated, or every time a device on the network is moved to a different part of the network. The whole network can now be run in software.
This hypervisor-based networking software (which will include security services as well) uses a controller to send network services to virtual switches and attaches the services to individual virtual machines (VMs) and containers. The result is a virtual network (The exact services will be determined by the policies already assigned to the VM/containers.). In this virtual network, whenever new VMs and containers are created, the appropriate policies are automatically applied to them. When VMs and containers move, their networking and security move with them. (You'll sometimes hear VMs and containers referred to as workloads, so we'll use that term here to familiarize you with it.)
Creating a virtual network on top of a physical network is known as overlay networking. Imagine two devices (or endpoints) on an organization’s network – Finance Department Laptop and Sales Department Laptop, for example. Both are connected to physical network ports. (VMs and containers can be endpoints, too.) Both laptops are given a virtual network ID (VNID) and assigned to a virtual network. Virtual switches then connect Finance Department Laptop to Sales Department Laptop via virtual links (software representations of physical links) that form a tunnel across the network. Each virtual link corresponds to a path in the underlying physical network.
Network virtualization works just as well in the cloud and can be managed by using a Cloud Management Platform (CMP) such as VMware’s vRealize Automation or an open-source option such as Apache CloudStack and OpenStack. Hypervisor-based network virtualization can be set up and run using a Graphical User Interface (GUI) and a Command-Line Interface (CLI) or using Application Programming Interfaces (APIs).
Network virtualization provides administrators with tremendous flexibility. It can be used for networks as small as two connected devices, or as large as networks spanning multiple sites of major enterprises. In addition, it is flexible enough to work with any cloud or cluster (or pod if you’re using a new application framework like Kubernetes) while having different virtual networks that can be associated with different workloads. VMware’s NSX for vSphere (NSX-V) virtual network and security product works with ESXi (a Type 1 hypervisor - i.e., one that runs directly on the host’s hardware, independent of the host’s operation system), while their NSX-T Data Center works with ESXi and with KVM (a Type 2 hypervisor running within the host’s operating system).
Virtual networks are not to be confused with virtual local area networks – VLANs. A VLAN takes the ports of a physical switch and groups (or isolates) them to fit a specific purpose. An organization might have its Finance Department on the first floor, HR on the second and third, Production on the fourth, Sales on the fifth, and printers scattered around the building. On one physical switch, five VLANs could be created for these separate functions, each with its own broadcast domain.
However, only a maximum of 4096 VLANS can be created on a Layer 2 network. (This is a reference to the OSI networking model, which has 7 layers that together describe the different communication functions of a networking system.) This may seem like a lot, but imagine being a company that gave each of its customers 5 VLANS: after customer 819, you would have no more VLANS, which would mean no new customers. Security is an issue since VLANs are separated from a logical perspective but are actually running through the same connection, and a security breach on one can affect them all. And every time a VLAN is extended, a time-consuming physical configuration is needed.
With network virtualization, on the other hand, network services beyond data transfer are also available – switching, routing, firewalling, and load balancing (Layer 3 to Layer 7 functions). The network in its entirety (Finance, HR, Production, Sales, and printers) can be recreated in software in seconds, and cloned or moved if needed; or snapshots representing the exact state of a network at a particular point in time can be created, saved, and used to recreate the network if required. Every networking and security service is virtualized (handled in software) and attached directly to individual workloads, reducing the need for physical configuration.

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