ZyXEL Communications ZYWALL USG 20 Manual page 512

Chapter 30 Content Filtering
External Content Filter Server Lookup Procedure
The content filter lookup process is described below.
Figure 302 Content Filter Lookup Procedure
A computer behind the ZyWALL tries to access a web site.
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The ZyWALL looks up the web site in its cache. If an attempt to access the web
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site was made in the past, a record of that web site's category will be in the
ZyWALL's cache. The ZyWALL blocks, blocks and logs or just logs the request
based on your configuration.
Use the Content Filter Cache screen to configure how long a web site address
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remains in the cache as well as view those web site addresses (see
on page
cache when the ZyWALL restarts.
If the ZyWALL has no record of the web site, it queries the external content filter
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database and simultaneously sends the request to the web server.
The external content filter server sends the category information back to the
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ZyWALL, which then blocks and/or logs access to the web site based on the
settings in the content filter profile. The web site's address and category are then
stored in the ZyWALL's content filter cache.
512
202). All of the web site address records are also cleared from the local
Section 9.15
ZyWALL USG 20/20W User's Guide