Web OS 10.0 Application GuideChapter 11: High Availability n 279212777-A, February 2002Using Spanning Tree Protocol to Eliminate LoopsVRRP generally requires Spanning Tree Protocol (STP) to be enabled in order to resolvebridge loops that usually occur in cross-redundant topologies, as shown in Figure 11-12. In thisexample, a number of loops are wired into the topology. STP resolves loops by blocking portswhere looping is detected.Figure 11-12 Cross-Redundancy Creates Loops, But STP Resolves ThemOne drawback to using STP with VRRP is the failover response time. STP could take as longas 45 seconds to re-establish alternate routes after a switch or link failure.Using VLANs to Eliminate LoopsWhen using VRRP, you can decrease failover response time by using VLANs instead of STPto separate traffic into non-looping broadcast domains. An example is shown in Figure 11-13:Figure 11-13 Using VLANs to Create Non-Looping TopologiesThis topology allows STP to be disabled. On the Alteon Web switches, IP routing allows traf-fic to cross VLAN boundaries. The servers use the Alteon Web switches as default gateways.For port failure, traffic is rerouted to the alternate path within one health check interval (con-figurable between 1 and 60 seconds, with a default of 2 seconds).Routers Alteon Web Switches Switches ServersInternetis for switch-to-switchand external routinggroups the first sub-switch with the AlteonWeb Switchesgroups the secondsub- switch with theAlteon Web switchesVLAN 1VLAN 2VLAN 3Routers Alteon Web Switches Switches ServersInternet
