One major advantage of virtualization is overall reduced cost:
- Less equipment is required—Virtualization enables server consolidation, which requires fewer physical devices and lowers maintenance costs.
- Less energy is consumed—Consolidating servers lowers the monthly power and cooling costs.
- Less space is required—Server consolidation reduces the amount of required floor space.
These are additional benefits of virtualization:
- Easier prototyping—Self-contained labs, operating on isolated networks, can be rapidly created for testing and prototyping network deployments.
- Faster server provisioning—Creating a virtual server is far faster than provisioning a physical server.
- Increased server uptime—Most server virtualization platforms now offer advanced redundant fault-tolerance features.
- Improved disaster recovery—Most enterprise server virtualization platforms have software that can help test and automate failover before a disaster happens.
- Legacy support—Virtualization can extend the life of OSs and applications, providing more time for organizations to migrate to newer solutions.
Hypervisors (14.2.7)
A hypervisor is a program, firmware, or hardware that adds an abstraction layer on top of the physical hardware. The abstraction layer is used to create virtual machines (VMs) that have access to all the hardware of the physical machine such as CPUs, memory, disk controllers, and NICs. Each of these virtual machines runs a complete and separate operating system. With virtualization, it is not uncommon for 100 physical servers to be consolidated as virtual machines on top of 10 physical servers that are using hypervisors.
Type 1 Hypervisors
Type 1 hypervisors are also called the “bare metal” approach because the hypervisors are installed directly on the hardware. Type 1 hypervisors are usually used on enterprise servers and data center networking devices.
With Type 1 hypervisors, the hypervisors are installed directly on the server or networking hardware. Then instances of an OS are installed on the hypervisor, as shown in Figure 14-6. Type 1 hypervisors have direct access to the hardware resources; therefore, they are more efficient than hosted architectures. Type 1 hypervisors improve scalability, performance, and robustness.
Figure 14-6 Type 1 Hypervisor
Type 2 Hypervisor
A Type 2 hypervisor is software that creates and runs VM instances. The computer on which a hypervisor is supporting one or more VMs is a host machine. Type 2 hypervisors are also called hosted hypervisors. The reason is that the hypervisor is installed on top of the existing OS, such as macOS, Windows, or Linux. Then one or more additional OS instances are installed on top of the hypervisor, as shown in Figure 14-7. A big advantage of Type 2 hypervisors is that management console software is not required.
Figure 14-7 Type 2 Hypervisor
Note
It is important to make sure that the host machine is robust enough to install and run the VMs so that it does not run out of resources.
Video—Software-Defined Networking (14.2.8)
Refer to the online course to view this video.
Network Virtualization (14.2.9)
Virtualization separates the operating system from the hardware. Server virtualization takes advantage of idle resources and consolidates the number of required servers. This also allows for multiple operating systems to exist on a single hardware platform. For example, in Figure 14-8, the previous eight dedicated servers are consolidated into two servers using hypervisors to support multiple virtual instances of the operating systems.
Figure 14-8 Consolidating Dedicated Servers
Network virtualization combines traditional networking hardware and software network resources into a software-based entity, which is a virtual network. Could the network infrastructure also benefit from virtualization? If so, then how? The answer is found in how a networking device operates using a data plane and a control plane.
Control Plane and Data Plane (14.2.10)
A network device contains the following planes:
- Control plane—This is typically regarded as the brains of a device. It is used to make forwarding decisions. The control plane contains Layer 2 and Layer 3 route forwarding mechanisms, such as the IPv4 and IPv6 routing tables, and the ARP table. Information sent to the control plane is processed by the CPU.
- Data plane—Also called the forwarding plane, this plane is typically the switch fabric connecting the various network ports on a device. The data plane of each device is used to forward traffic flows. Routers and switches use information from the control plane to forward incoming traffic out the appropriate egress (outgoing) interface. Information in the data plane is typically processed by a special data plane processor without the CPU getting involved.
Figure 14-9 illustrates how Cisco Express Forwarding (CEF) uses the control plane and data plane to process packets.
Figure 14-9 Cisco Express Forwarding
