Chapter 10 Interfaces
ZyWALL USG Series User’s Guide
395
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.
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
Table 130 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
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