ZyXEL Communications ZyWall 110 User Manual page 257

Since WAN 2 has a smaller load balancing index (meaning that it is less utilized than WAN 1), the
ZyWALL/USG will send the subsequent new session traffic through WAN 2.
Table 109 Least Load First Example
OUTBOUND
INTERFACE
AVAILABLE (A)
WAN 1 512 K
WAN 2 256 K
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 traffic on that interface. This queue then moves to the back of the list. The next queue is
given an equal amount of bandwidth, and then moves to the end of the list; and so on, depending
on the number of queues being used. This works in a looping fashion until a queue is empty.
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, the Weighted
Round Robin (WRR) algorithm sets the ZyWALL/USG 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 chances to transmit 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/USG to distribute the network traffic between the two interfaces by
setting the weight of wan1 and wan2 to 2 and 1 respectively. The ZyWALL/USG assigns the traffic of
two sessions to wan1 and one session's traffic to wan2 in each round of 3 new sessions.
Figure 175 Weighted Round Robin Algorithm Example
Spillover
The spillover load balancing algorithm sends network traffic to the first interface in the trunk
member list until the interface's maximum allowable load is reached, then sends the excess
network traffic of new sessions to the next interface in the trunk member list. This continues as
long as there are more member interfaces and traffic to be sent through them.
Suppose the first trunk member interface uses an unlimited access Internet connection and the
second is billed by usage. Spillover load balancing only uses the second interface when the traffic
load exceeds the threshold on the first interface. This fully utilizes the bandwidth of the first
interface to reduce Internet usage fees and avoid overloading the interface.
In this example figure, the upper threshold of the first interface is set to 800K. The ZyWALL/USG
sends network traffic of new sessions that exceed this limit to the secondary WAN interface.
Chapter 9 Interfaces
MEASURED (M)
412 K
198 K
ZyWALL/USG Series User's Guide
257
LOAD BALANCING INDEX
(M/A)
0.8
0.77