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Making Layer 7 Work for You: Page 6 of 7

Content networking will continue to be a major part of a successful Web infrastructure design, especially with the emergence of Web services and XML for e-business. Load balancers and other Layer 7 content networking devices from F5 Networks are already digging even deeper into application traffic, giving you more control in managing your Web traffic and making it easier to develop automated e-business and e-commerce applications. So it's important to know the ins and outs of how to design your Web infrastructure with these devices.

Technology editor Lori MacVittie has been a software developer, a network administrator and a member of the technical architecture team for a global transportation and logistics organization. Write to her at [email protected].

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You can't talk load balancing without considering failover scenarios. Because a load balancer often is the single point of entry into your Web infrastructure, you need a backup load balancer to pick up the slack when your primary device fails. Beware, though, that adding a second device means deciding on yet another configuration.

The two main configurations for load-balancing failover are active-active and active-standby. In an active-active failover configuration, two load balancers can service requests for the same IP address. That means your Web infrastructure can serve more clients simultaneously, and latency is reduced in the failover process.

In an active-standby configuration, one load balancer is responsible for serving requests, and a secondary device takes over when the first one fails. When the standby load balancer steps in after a failure, it assumes the primary device's IP and MAC addresses, and handles all requests until the primary device is restored. The trade-off with this approach is that the failover process can take several seconds, during which time any incoming requests for Web content could get rejected.