ZyXEL Communications ZyWALL5UTM 4.0 User Manual

ZyWALL 5/35/70 Series User’s Guide

Chapter 7 WAN Screens

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The following figure depicts an example where both the WAN ports on the ZyWALL are 
connected to the Internet. The configured available outbound bandwidths for WAN 1 and 
WAN 2 are 512K and 256K respectively.

Figure 47   Least Load First Example 

If the outbound bandwidth utilization is used as the load balancing index and the measured 
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. 

Since WAN 2 has a smaller load balancing index (meaning that it is less utilized than WAN 1), 
the ZyWALL will send the subsequent new session traffic through WAN 2.

Table 30   Least Load First: Example 1

WAN 1

512 K

412 K

0.8

WAN 2

256 K 

198 K

0.77

This example uses the same network scenario as in 

, but uses both the 

outbound and inbound bandwidth utilization in calculating the load balancing index.  If the 
measured inbound stream throughput for both WAN 1 and WAN 2 is 102K, the ZyWALL 
calculates the average load balancing indices as shown in the table below. 

Since WAN 1 has a smaller load balancing index (meaning that it is less utilized than WAN 2), 
the ZyWALL will send the next new session traffic through WAN 1.

Table 31   Least Load First: Example 2

WAN 1

512 K

412 K

256 K 

102 K

( 0.8 + 0.4) / 2 = 0.6

WAN 2

256 K 

198 K

128 K 

102 K

 ( 0.77 + 0.8 ) / 2 = 0.79