Cơ sở hạ tầng giao dịch với cân bằng tải và các thành phần khác được kết nối với thế giới bên ngoài. Có rất nhiều kịch bản cơ sở hạ tầng có thể, chẳng hạn như các ISP, Thuê vị trí trung tâm dữ liệu trong lưu trữ của đường dây cho thuê, và nhiều hơn nữa. | 64 Chapter 7 NAT-Based SLB Network Architecture Web Server ws-1 Web Server ws-2 Web Server Web Server ws-3 ws-4 Figure 7-2. NAT-based route-path one-armedSLB V LANs as well. There is a clear delineation and demarcation point for the two separate networks making troubleshooting in many cases much easier. Bridge-Path and DSR Because NAT from one network to another is a Layer 3 function bridge-path isn t an option for NAT-based SLB. For NAT to work the load balancer must have interfaces on two networks and bridge-path generally involves only one network. DSR is not as common in a NAT-based scenario as it is in a flat-based setup but it is possible. Unlike flat-based scenarios a Layer 3 device is required in addition to the load balancer and Layer 2 infrastructure to work with DSR. As per a DSR scenario the packets have already been rewritten on the way out of the actual servers with no need for any more processing. The Layer 3 device simply forwards the Implementation 65 packets from one network to another a process that is resource-intensive but saves the load balancer some work. In Figure 7-3 we see an example of a NAT-based configuration with DSR. Figure 7-3. NAT-based network topology with DSR The redundancy component was removed to better show how DSR would fit into this type of scenario. A packet comes to the load balancer step 1 and is sent to a web server such as ws-3 step 2 . The web server then sends the packet out already rewritten step 3 but it still needs to be forwarded to the public network so it can get to the Internet. The Layer 3 device forwards the packet unchanged to the public network and then on to its destination step 4 without adding any additional load to the load balancer. The actual load on the Layer 3 device is minimal since all it is doing is forwarding packets with no processing. Why NAT-Based There are several advantages to NAT-based SLB most of which involve the extra security that
