A virtual network is a computer network
that consists, at least in part, of virtual network links. A virtual
network link is a link that does not consist of a physical (wired or
wireless) connection between two computing devices but is implemented
using methods of network virtualization.
The two most common forms of network virtualization are protocol-based virtual networks (such as VLANs, VPNs, and VPLSs) and virtual networks that are based on virtual devices (such as the networks connecting virtual machines inside a hypervisor). In practice, both forms can be used in conjunction.
Virtual LANs (VLANs) are logical local area networks
(LANs) based on physical LANs. A VLAN can be created by partitioning a
physical LAN into multiple logical LANs using a VLAN ID. Alternatively,
several physical LANs can function as a single logical LAN. The
partitioned network can be on a single router, or multiple VLANs can be on multiple routers just as multiple physical LANs would be. A VLAN can be on a VPN.
A virtual private network (VPN) consists of multiple remote end-points (typically routers, VPN gateways
of software clients) joined by some sort of tunnel over another
network, usually a third party network. Two such end points constitute a
'Point to Point Virtual Private Network' (or a PTP VPN). Connecting
more than two end points by putting in place a mesh of tunnels creates a
'Multipoint VPN'.
A VPLS (Virtual Private LAN Service) is a specific type of Multipoint VPN. VPLS are divided into Transparent LAN Services
(TLS) and Ethernet Virtual Connection Services. A TLS sends what it
receives, so it provides geographic separation, but not VLAN subnetting.
An EVCS adds a VLAN ID, so it provides geographic separation and VLAN
subnetting.
A common example of a virtual network that is based on virtual
devices is the network inside a hypervisor where traffic between virtual
servers are routed using virtual switches (vSwitches) along with virtual routers and virtual firewalls
for network segmentation and data isolation. Such networks can use
non-virtual protocols such as Ethernet as well as virtualization
protocols such as the VLAN protocol IEEE 802.1Q.
A virtual wireless network is a collection of wireless access points
behaving as if they were only one. They all appear to have the same MAC
address and the same channel, so the wireless client never needs to do
handovers. Handovers are disruptive to communication. Though the client
might not note it much when web browsing, he will definitely note it
when streaming a video feed and handing over.
Source: wikipedia
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