ZyXEL Communications USG40 User Manual page 830

Chapter 43 System
An open DNS server is a DNS server which is willing to resolve recursive DNS queries from anyone
on the Internet.
In a DNS amplification attack, an attacker sends a DNS name lookup request to an open DNS
server with the source address spoofed as the victim's address. When the DNS server sends the
DNS record response, it is sent to the victim. Attackers can request as much information as possible
to maximize the amplification effect.
Configure the Security Option Control section in the Configuration > System > DNS screen
(click Show Advanced Settings to display it) if you suspect the ZyWALL/USG is being used (either
by hackers or by a corrupted open DNS server) in a DNS amplification attack.
Figure 575 Configuration > System > DNS
ZyWALL/USG Series User's Guide
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