Load Balancing Introduction; Load Balancing Algorithms; Least Load First; Example 1 - ZyXEL Communications ZyWall 35 User Manual

ZyWALL 35 User's Guide

7.3 Load Balancing Introduction

On the ZyWALL, load balancing is the process of dividing traffic loads between the two
WAN interfaces (or ports). This allows you to improve quality of services and maximize
bandwidth utilization.
See also policy routing to provide quality of service by dedicating a route for a specific traffic
type and bandwidth management to specify a set amount of bandwidth for a specific traffic
type on an interface.

7.4 Load Balancing Algorithms

The ZyWALL uses three load balancing methods (Least Load First, Weighted Round
Robin and Spillover) to decide which WAN port the traffic for a session
should use.
The following sections describe each load balancing method. The available bandwidth you
configure on the ZyWALL refers to the actual bandwidth provided by the ISP and the
measured bandwidth refers to as the bandwidth an interface is currently using.

7.4.1 Least Load First

The least load first algorithm uses the current (or recent) outbound and/or inbound bandwidth
utilization of each WAN interface as the load balancing index(es) when making decisions
about to which WAN interface a new LAN-originated session is to be distributed. The
outbound bandwidth utilization is defined as the measured outbound throughput over the
available outbound bandwidth and the inbound bandwidth utilization is defined as the
measured inbound throughput over the available inbound bandwidth.

7.4.1.1 Example 1

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.
1. In the load balancing section, a session may refer to normal connection-oriented, UDP and
SNMP2 traffic.
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1
(from the LAN)
Chapter 7 WAN Screens