ZyXEL Communications USG40 User Manual page 642

Figure 447 Content Filter Lookup Procedure
A computer behind the ZyWALL/USG tries to access a web site.
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The ZyWALL/USG looks up the web site in its cache. If an attempt to access the web site was made
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in the past, a record of that web site's category will be in the ZyWALL/USG's cache. The ZyWALL/
USG 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 remains in the
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cache as well as view those web site addresses. All of the web site address records are also cleared
from the local cache when the ZyWALL/USG restarts.
If the ZyWALL/USG has no record of the web site, it queries the external content filter database and
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simultaneously sends the request to the web server.
The external content filter server sends the category information back to the ZyWALL/USG, which
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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/USG's content filter cache.
Chapter 36 Content Filtering
ZyWALL/USG Series User's Guide
642