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Making Layer 7 Work for You: Page 3 of 7

Content networking devices usually have to be in proxy mode to process SSL sessions on the Web. A load balancer either decrypts the data itself or has a third-party product do it, so it can examine the traffic and make a routing decision. It then has to re-encrypt its response to the client's request with SSL. Some devices can do this in transparent mode, but that means more latency.

In transparent mode, the load balancer or other content networking device operates like the reverse Web cache, where a router redirects requests to a specific port (usually Port 80) or a specific port/IP address combination to a caching device. This is a less intrusive configuration than proxy mode because it requires little change to the network infrastructure.

The main difference between proxy and transparent mode is that in proxy mode the content networking device terminates the session, whereas the Web server terminates the session when the content networking device is in transparent mode. In both cases, the content networking device remains responsible for determining which Web server should fulfill the client request (see graphic "To Proxy or Not To Proxy").

The topology of your network dictates where the content networking device physically sits. There are three server-farm topologies: inline, one-arm and side-arm.

When a content networking device is deployed in an inline network topology, it sits between the router and the network switch that's physically connected to the server farm. The downside of this configuration is that all traffic must return via the Layer 7 device regardless of whether the device needs to see the traffic on the egress route. If the device can't handle high throughput, performance will suffer.

Deploying and configuring an inline topology with a load balancer in proxy mode is simple. But high-availability Web environments with this topology need an additional load balancer to support failover and to avoid a single point of failure (see "Sharing the Load," page 71). The inline topology diagram above illustrates this type of setup.