BROCADE IP PRIMER

Load Balancing Basics5With the rise of the Internet, load balancing is more popular than ever. It allowsyou to share the load of your traffic across many different servers. It also providesredundancy to your infrastructure. In this chapter, we'll go over many ofthe basic aspects of load balancing. In Section IV, we'll go over the specifics ofhow to configure them.The Virtual IP (VIP) AddressWhen you configure a device to be on a TCP/IP network, you will configure anIP address for the device. Whenever that device communicates on the network,it uses its IP address as the source IP address in the IP header of thepacket. Whenever other devices on the network want to communicate to thisdevice, they will use the device's IP address as the destination IP address inthe IP header of the packet.What if we have five servers that all provide the same function? We want allfive to be used by our clients, but we don't want our clients to have to rememberfive different IP addresses. We also don't want them to have to use trialand error to make sure that the one server they chose is actually active. Hereis where we would deploy load balancing, and the first element needed is a virtualIP address (VIP).A VIP is an IP address that is not assigned to a specific NIC. In fact, it's notassigned to a specific host. It is an address that the clients would communicatewith. Typically, the actual device that answers for the VIP is the loadbalancer. But traffic coming to the VIP will actually be handed off to one of theservers being load balanced. The server will actually do the processing of thedata.In our previous example, where we wanted our clients to use all five of ourservers, the clients would now communicate with a VIP. The VIP would behosted by the load balancer. When a request is sent by the clients, the loadbalancer will forward the request to one of the five servers. It will also be theload balancer's job to keep track of which servers may or may not be responding.This is so the client won't have to. That way, if a server goes down, theclient may never know.Brocade IP Primer 97