...the continuous availability of applications that are deployed across multiple production servers through the use of secondaryservers running on virtual machines on a single virtual host”. This approach “brings the cost benefits of server consolidation...
http://www.continuitycentral.com/news04730.html
...filtering mechanism is hooked into the IP stack, permitting near switching of IP address between the Primary and Secondaryservers. Mechanisms relying adding or removing IP addresses from Network Cards require considerably longer to switch. ...
http://www.findwhitepapers.com/whitepaper278/