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Chapter 20 DNS
ZyWALL 2 Plus User’s Guide
349
20.7 DNS Cache
DNS cache is the temporary storage area where a router stores responses from DNS servers.
When the ZyWALL receives a positive or negative response for a DNS query, it records the
response in the DNS cache. A positive response means that the ZyWALL received the IP
address for a domain name that it checked with a DNS server within the five second DNS
timeout period. A negative response means that the ZyWALL did not receive a response for a
query it sent to a DNS server within the five second DNS timeout period.
When the ZyWALL receives DNS queries, it compares them against the DNS cache before
querying a DNS server. If the DNS query matches a positive entry, the ZyWALL responses
with the IP address from the entry. If the DNS query matches a negative entry, the ZyWALL
replies that the DNS query failed.
20.8 Configure DNS Cache
To configure your ZyWALL’s DNS caching, click ADVANCED > DNS > Cache. The screen
appears as shown.
Figure 223 ADVANCED > DNS > Cache
The following table describes the labels in this screen.
Table 115 ADVANCED > DNS > Cache
LABEL DESCRIPTION
DNS Cache Setup
Cache Positive DNS
Resolutions
Select the check box to record the positive DNS resolutions in the cache.
Caching positive DNS resolutions helps speed up the ZyWALL’s processing of
commonly queried domain names and reduces the amount of traffic that the
ZyWALL sends out to the WAN.