Virtual IP address

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A virtual IP address (VIP or VIPA) is an IP address that is not connected to a specific computer or network interface card (NIC) on a computer. Incoming packets are sent to the VIP address, but all packets travel through real network interfaces.

VIPs are mostly used for connection redundancy; a VIP address may still be available if a computer or NIC fails because an alternative computer or NIC replies to connections.^[1]

[edit] Example

A particular service is served by a collection of application servers. A virtual IP address is created so that applications using this service may direct their requests to that address without specifying the particular server to use. A load balancer such as a Citrix NetScaler serves this IP and redirects traffic using a hash or round robin algorithm to the backend servers. In case of a server failure, the configuration can be modified or automatically set so that traffic no longer goes to the failing server. From the user's perspective, uptime is maintained.