Web OS 10.0 Application Guide326 n Chapter 13: Firewall Load Balancing 212777-A, February 2002Four-Subnet FWLBThe four-subnet FWLB method is often deployed in large networks that require high-availabil-ity solutions. This method uses filtering, static routing, and Virtual Router Redundancy Proto-col (VRRP) to provide parallel firewall operation between redundant Web switches.Figure 13-5 shows one possible network topology using the four-subnet method:Figure 13-5 Four-Subnet FWLB TopologyThis network is classified as a high-availability network because no single component or linkfailure could cause network resources to become unavailable. Simple switches and verticalblock interswitch connections are used to provide multiple paths for network failover. Nor-mally the interswitch link between the primary and secondary Web switches is configured onport 9 of the Web switch. However, the interswitch links may trunked together with multipleports for additional protection from failure.N OTE – Other topologies that use internal hubs, or diagonal cross-connections between theWeb switches and simple switches are also possible. While such topologies may resolve net-working issues in special circumstances, they can make configuration more complex and cancause restrictions on the use of advanced features such as Active-Active VRRP, free-metricFWLB, or Content Intelligent Switching. Alternate topologies are explored in more detail inWeb OS FWLB white papers, but are not within the scope of this manual.Subnet 1 Subnet 2 Subnet 3 Subnet 4Dirty Side Clean SideInternetRouters SimpleSwitches SimpleSwitchesFirewallsPrimarySecondaryWeb SwitchPrimarySecondaryWeb Switch Servers
