Inbound Load Balancing; Inbound Load Balancing Overview; What You Can Do In This Chapter - ZyXEL Communications ZyWall USG20-VPN User Manual

18.1 Inbound Load Balancing Overview

Inbound load balancing enables the USG to respond to a DNS query message with a different IP
address for DNS name resolution. The USG checks which member interface has the least load and
responds to the DNS query message with the interface's IP address.
In the following figure, an Internet host (A) sends a DNS query message to the DNS server (D) in
order to resolve a domain name of www.example.com. DNS server D redirects it to the USG (Z)'s
WAN1 with an IP address of 1.1.1.1. The USG receives the DNS query message and responds to it
with the WAN2's IP address, 2.2.2.2, because the WAN2 has the least load at that moment.
Another Internet host (B) also sends a DNS query message to ask where www.example.com is. The
USG responds to it with the WAN1's IP address, 1.1.1.1, since WAN1 has the least load this time.
Figure 200 DNS Load Balancing Example
W
W

18.1.1 What You Can Do in this Chapter

• Use the Inbound LB screen (see
load balancing rules.
• Use the Inbound LB Add/Edit screen (see
load balancing rule.
C

Inbound Load Balancing

Where is
A:
www.example.com?
Z:
It's 2.2.2.2.
2
1.1.1.1
2.2.2.2 3
Z
Where is
B:
www.example.com?
Z:
It's 1.1.1.1
2
1.1.1.1
3
2.2.2.2
Z
Section 18.2 on page
USG20(W)-VPN Series User's Guide
292
HAPTER
D
Where is
A:
www.example.com?
D:
1 Ask 1.1.1.1.
Internet
D
Where is
B:
www.example.com?
D:
1
Ask 1.1.1.1.
Internet
293) to view a list of the configured DNS
Section 18.2.1 on page 294) to add or edit a DNS
1 8
A
B