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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. == See also == * Overlay network * Virtual circuit * Virtual machine * Virtual firewall 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「virtual network」の詳細全文を読む スポンサード リンク
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