ZyXEL Communications ZyWall USG20-VPN User Manual page 220

You can also use trunks with policy routing to send specific traffic types through the best WAN
interface for that type of traffic.
• If that interface's connection goes down, the USG can still send its traffic through another
interface.
• You can define multiple trunks for the same physical interfaces.
LAN user A logs into server B on the Internet. The USG uses wan1 to send the request to server B.
1
The USG is using active/active load balancing. So when LAN user A tries to access something on the
2
server, the request goes out through wan2.
The server finds that the request comes from wan2's IP address instead of wan1's IP address and
3
rejects the request.
If link sticking had been configured, the USG 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 USG 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
configure on the USG 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 USG 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 144 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 USG calculates
the load balancing index as shown in the table below.
Chapter 9 Interfaces
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The available bandwidth you
.