ServerIron ADX Server Load Balancing Guide
Release 12.0.00
June 15, 2009

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Server Load Balancing

Server Load Balancing
This chapter contains the following sections:
DSR
Server Load Balancing (SLB) is based on associations between real servers and virtual servers. The real servers are your application servers. The virtual servers have one or more Virtual IP addresses (VIPs). You associate a real server with a virtual server by binding TCP/UDP ports on the real servers with TCP/UDP ports on the virtual server. When a client sends a TCP/UDP request for a port on the virtual server, the ServerIron ADX sends the client’s request to the real server. The client is unaware of the real servers behind the virtual server but does experience enhanced throughput and availability for TCP/UDP services.
SLB maps one logical (virtual) server connection to multiple physical (real) servers. This allows a single IP address (virtual server IP address) can serve as the connection point for multiple TCP/UDP services such as HTTP, FTP or Telnet rather than each of the services requiring a different IP address for each service. These services can be located on a single server or across multiple servers.
Figure 2.1
In Figure 2.1, a company establishes a Web site with the URL of www.alterego.com. The Web site is mapped to the virtual IP address 207.95.55.1, defined on a ServerIron ADX. All inquiries made to that Web site by users on the Internet or the company's Intranet use either the URL or virtual IP address to reach the company's Web site.
Once these inquiries are received at the company site, the requests are handled by one of four separate physical (real) Web servers that the system administrator has mapped to the virtual IP address. The addresses of the four physical (real) Web servers are unknown and unseen to those users who send the inquiries. The only address the users ever see for the Web site is the virtual IP address.

Server Load Balancing

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