BROCADE IP PRIMER

Predictors• Round-robin. This is the simplest of load balancing methods. The incomingpacket goes to the next real server in line. When the real servers arebound to the VIP, they are bound in a certain order. It is that order thatthis predictor will use. If a real server is down, it will not be included in theround-robin rotation.• Weighted. Here, the administrator defines a weight on each real server.This is useful if you have real servers of varying ability. Let's say you havethree real servers. One is very new, and very fast. The other is okay. Thethird is aging rapidly. Ideally, you want more traffic to go to the new server,and less to go to the weakest. You could configure weights like this:— real server1 (fast) - weight 10— real server2 (medium) - weight 5— real server3 (slow) - weight 1In this example, you would add all of the weights together (10 + 5 + 1 =16). This tells you that out of every sixteen incoming packets theServerIron receives, server1 will get ten, server2 will get five, and server3will get one.• Server response time only. The ServerIron uses a special algorithm towatch the response time of the real servers. It watches both health checkresponses and client responses. It gauges its time by watching TCP SYNand TCP SYN/ACK segments. The server with the fastest response time isusually selected, but if a slower server has not been selected in over oneminute, the ServerIron will send the next packet to it. It will use this transactionto remeasure the server's response time.• Least connection and server response time weight (formerly “ResponseTime/Least Connections”). This is similar to weighted. The administratorwill manually configure a “least connection weight” and a “serverresponse weight” on each of its real servers. Based on the combination ofthese weights, the next real server will be selected. Configuring a higherweight biases the ServerIron toward that real server.• Least local connections (chassis only). On an individual BP basis, theServerIron chooses the real server with the least active client connections.Specifically, the ServerIron selects the real server with the fewestnumber of active client connections distributed from that specific BP.• Least local sessions (chassis only). On an individual BP basis, theServerIron chooses the real server with the least number of active clientsessions distributed from a specific BP.• Dynamic Weighted Predictor. TrafficWorks provides a dynamic weightedpredictor that enables ServerIron to make load balancing decisions usingreal time server resource usage information, such as CPU utilization andmemory consumption. The ServerIron retrieves this information (throughthe SNMP protocol) from MIBs available on the application servers. Toachieve this capability, a software process in ServerIron, named SNMPBrocade IP Primer 333