ZyXEL Communications USG 2000 User Manual

 Chapter 14 Trunks

ZyWALL USG 2000 User’s Guide

The ZyWALL is using active/active load balancing. So when LAN user A tries to 
access something on the server, the request goes out through ge3.

The server finds that the request comes from ge3’s IP address instead of  ge2’s IP 
address and rejects the request.

If link sticking had been configured, the ZyWALL would have still used ge2 to send 
LAN user A’s request to the server and server would have given the user A access.

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 session

2

. 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. 

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 267   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.