Web OS 10.0 Application GuideChapter 11: High Availability n 253212777-A, February 2002Failover MethodsWith service availability becoming a major concern on the Internet, service providers areincreasingly deploying Internet traffic control devices, such as Web switches, in redundantconfigurations. Traditionally, these configurations have been hot-standby configurations,where one switch is active and the other is in a standby mode. A non-VRRP hot-standby con-figuration is shown in the figure below:Figure 11-3 A Non-VRRP, Hot-Standby ConfigurationWhile hot-standby configurations increase site availability by removing single points-of-fail-ure, service providers increasingly view them as an inefficient use of network resourcesbecause one functional Web switch sits by idly until a failure calls it into action. Service pro-viders now demand that vendors’ equipment support redundant configurations where alldevices can process traffic when they are healthy, increasing site throughput and decreasinguser response times when no device has failed.Web OS high availability configurations are based on VRRP. The Web OS implementation ofVRRP includes proprietary extensions to accommodate Layer 4 though Layer 7 Web switchingfeatures.The Web OS implementation of VRRP supports three modes of high availability: Active-Standby Active-Active Hot-StandbyThe first mode, active-standby, is based on standard VRRP, as defined in RFC 2338. The sec-ond and third modes, active-active and hot-standby, are based on proprietary Web OS exten-sions to VRRP. Each mode is described in detail in the following sections.Intranet ServersNFS ServerA BIntranet ClientsClient SwitchesPrimary Web SwitchIP: 200.200.200.100Secondary Web SwitchIP: 200.200.200.101Active LinksBackup LinksInter-switchLink
