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ZyWALL 110/310/1100 Series User’s Guide 247
CHAPTER 17
Inbound Load Balancing
17.1 Inbound Load Balancing Overview
Inbound load balancing enables the ZyWALL to respond to a DNS query message with a different IP
address for DNS name resolution. The ZyWALL 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 ZyWALL
(Z)’s WAN1 with an IP address of 1.1.1.1. The ZyWALL 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
ZyWALL responds to it with the WAN1’s IP address, 1.1.1.1, since WAN1 has the least load this
time.
Figure 145 DNS Load Balancing Example
17.1.1 What You Can Do in this Chapter
•Use the Inbound LB screen (see Section 17.2 on page 248) to view a list of the configured DNS
load balancing rules.
Internet
Where is
www.example.com?
Ask 1.1.1.1.
A:
D:
A
D
1.1.1.1
2.2.2.2
W
Z
Where is
www.example.com?
It’s 2.2.2.2.
A:
Z:
1
2
3
Internet
B
D
1.1.1.1
2.2.2.2
W
Z
1
2
3
Where is
www.example.com?
Ask 1.1.1.1.
B:
D:
Where is
www.example.com?
It’s 2.2.2.2.
B:
Z: