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Chapter 11 Trunks
ZyWALL USG 100/200 Series User’s Guide
271
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 188 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.
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.
Weighted Round Robin
The Weighted Round Robin (WRR) algorithm is best suited for situations when the
bandwidths set for the two WAN interfaces are different. Similar to the Round Robin (RR)
algorithm (see Section 11.3 on page 275), the Weighted Round Robin (WRR) algorithm sets
the ZyWALL to send traffic through each WAN interface in turn. In addition, the WAN
interfaces are assigned weights. An interface with a larger weight gets more of the traffic than
an interface with a smaller weight.
For example, in the figure below, the configured available bandwidth of WAN1 is 1M and
WAN2 is 512K. You can set the ZyWALL to distribute the network traffic between the two
interfaces by setting the weight of WAN1 and WAN2 to 2 and 1 respectively. The ZyWALL
assigns the traffic of two sessions to WAN1 for every session's traffic assigned to WAN2.
Table 86 Least Load First Example
INTERFACE
OUTBOUND
LOAD BALANCING INDEX
(M/A)
AVAILABLE (A) MEASURED (M)
WAN 1 512 K 412 K 0.8
WAN 2 256 K 198 K 0.77