Chapter 12 Trunks

2The ZyWALL is using active/active load balancing. So when LAN user A tries to access something on the server, the request goes out through wan2.

3The server finds that the request comes from wan2’s IP address instead of wan1’s IP address and rejects the request.

If link sticking had been configured, the ZyWALL 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 ZyWALL can use to decide which interface the traffic (from the LAN) should use for a session2. The available bandwidth you configure on the ZyWALL 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 ZyWALL 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 169 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 ZyWALL calculates the load balancing index as shown in the table below.

2.In the load balancing section, a session may refer to normal connection-oriented, UDP or SNMP2 traffic.

 

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ZyWALL USG 50 User’s Guide