ZyXEL USG110/210/310 User Guide - Page 395
Load Balancing Algorithms, Least Load First, Weighted Round Robin
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Chapter 10 Interfaces If link sticking had been configured, the Zyxel Device would have still used wan1 to send LAN user A's request to the server and server would have given the user A access. Load Balancing Algorithms The following sections describe the load balancing algorithms the Zyxel Device can use to decide which interface the traffic (from the LAN) should use for a session. In the load balancing section, a session may refer to normal connection-oriented, UDP or SNMP2 traffic. The available bandwidth you configure on the Zyxel Device refers to the actual bandwidth provided by the ISP and the measured bandwidth refers to the bandwidth an interface is currently using. Least Load First The least load first algorithm uses the current (or recent) outbound bandwidth utilization of each trunk member interface as the load balancing index(es) when making decisions about to which interface a new session is to be distributed. The outbound bandwidth utilization is defined as the measured outbound throughput over the available outbound bandwidth. Here the Zyxel Device has two WAN interfaces connected to the Internet. The configured available outbound bandwidths for WAN 1 and WAN 2 are 512K and 256K respectively. Figure 275 Load Balancing Least Load First Example The outbound bandwidth utilization is used as the load balancing index. In this example, the measured (current) outbound throughput of WAN 1 is 412K and WAN 2 is 198K. The Zyxel Device calculates the load balancing index as shown in the table below. Since WAN 2 has a smaller load balancing index (meaning that it is less utilized than WAN 1), the Zyxel Device will send the subsequent new session traffic through WAN 2. Table 130 Least Load First Example INTERFACE OUTBOUND AVAILABLE (A) WAN 1 512 K WAN 2 256 K MEASURED (M) 412 K 198 K LOAD BALANCING INDEX (M/A) 0.8 0.77 Weighted Round Robin Round Robin scheduling services queues on a rotating basis and is activated only when an interface has more traffic than it can handle. A queue is given an amount of bandwidth irrespective of the incoming ZyWALL USG Series User's Guide 395
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