 connecting all the servers to the firewall is a Cisco Content Switch. For our examples, we'll use a Cisco Content Switching Module (CSM) blade in a Cisco 6509 Catalyst switch. One of the real benefits of using an integrated service module like this is that it can be completely removed from the network using only command-line instructions. Types of Load Balancing Server load balancing is only one of many ways to accomplish the goal of multiple servers responding as one. Let's look at some different possibilities, and the pros and cons of each: DNS load balancing As the name implies, balancing is done with DNS. A single name resolves to multiple other names or IP addresses. These real names or IP addresses are then hit in a round-robin manner. Very simple to configure and understand. Cons: No intelligence other than round-robin. No way to guarantee connection to the same server twice if needed (sticky connections). DNS cannot tell if a server has become unavailable. Load may not be evenly distributed, as DNS cannot tell how much load is present on the servers. Each server requires a public IP address, in the case of publicly available web servers. Bridged load balancing Load balancing at layer two, or bridged load balancing, is a very simple model. A virtual IP address is created in the same IP network as the real servers. Packets destined for the virtual IP address are forwarded to the real servers. Pros: Can be inserted into an existing network, with no additional IP networks required. Possibly easier to understand for simple networks. Usually less expensive than a routed model. Chapter 27: Server Load-Balancing Technology Cons: Layer-2 issues including loops and spanning-tree problems can arise if the solution is not designed carefully. Can be harder to understand for people used to layer-3 environments. Usually limited to a single local network. Routed load balancing Load balancing at layer three, or routed load balancing, is slightly more complex than bridged load balancing. In this model, the virtual IP addr