Virtualization is the abstraction of computing and network resources. In the computing world, there can be various degrees of virtualization:
Segmenting a common network into separate virtual networks to isolate user traffic within individual network domains involves logical separation of data-plane (and some control-plane) functionality. There can be several forms of network virtualization:
- Virtual LANs (VLANs) - Separate L2 LAN broadcast domains.
- Virtual Routing Forwarding (VRFs) - Separate L3 routing domains.
- Virtual Private Networks (VPNs) - Creating virtual circuits in a shared network. Commonly deployed VPN technologies include MPLS-VPN, IPsec-VPN, etc.
Segmenting a device into separate logical independent entities.
- Virtual Contexts - Used on firewalls, load balancers, and other application networking platforms. Involves logical separation of data-plane, and some separation of configuration and management plane. Available on Cisco FWSM, ACE, etc.
- Secure Domain Routers (SDR) - Creating separate logical routers, each using its own route processors and line cards, within the same physical chassis. SDRs are isolated from each other in terms of their resources, performance, and availability. Available in Cisco IOS-XR platforms.
- Virtual Device Contexts (VDCs) - Logical separation of control-plane, data-plane, management, resources, and system processes that enables collapsing multiple logical networks into a single physical infrastructure. Available on Cisco Nexus 7000 platforms.
Hardware assisted virtualization simulates a complete hardware environment, or Virtual Machine (VM), in which an unmodified "guest" operating system executes in complete isolation. A physical computer server is partitioned into multiple logical servers so that each has the appearance and capabilities of running on its own dedicated machine. Each virtual server can run its own full-fledged operating system, and each server can be independently rebooted. With hardware-assisted full virtualization, multiple low usage servers can be virtualized - transformed into a Virtual Machine - and multiple VMs can be run simultaneously on the same physical server. VMs can also be moved from one server to another for load balancing or disaster recovery.
Desktop Virtualization or Virtual Desktop Infrastructure (VDI)
VDI is a server-centric computing model that provides the ability to host and centrally manage desktop virtual machines in the data center while giving end users a full PC desktop experience.
Storage virtualization is the process of abstracting logical storage from physical storage. This abstraction can be done at any layer of the storage software and hardware stack. Virtualization of storage helps achieve location independence by abstracting the physical location of the data. The virtualization system presents to the user a logical space for data storage and itself handles the process of mapping it to the actual physical location. The logical storage can be a partition, volume, or virtual disk (vdisk). The abstraction can be host-based, storage device-based, or network-based. Storage area networks (SANs) can also be virtualized into zones and Virtual SAN (VSANs). Zoning is a distributed service common throughout the Fibre Channel (FC) fabric and prevents devices from communicating with other unauthorized devices. A VSAN provides the ability to create separate virtual fabrics on top of the same redundant physical infrastructure.