The Anti-Virus Cache - D-Link NetDefendOS User Manual

3. Select the Anti-Virus option
4. Enable Anti-Virus
5. Set the Anti-Virus Profile to av_audit_profile
6. Select OK

6.5.5. The Anti-Virus Cache

All anti-virus scans performed with the HTTP ALG use a common anti-virus cache. This cache is an
allocation of volatile memory which contains the URLs of recently scanned files that were
blocked by the anti-virus mechanism.
If a virus has been detected using the cache, the URLForbidden banner file is displayed indicating
that the URL has been blocked. This is the same banner file which is used with Web Content
Filtering (WCF) and can be modified by the administrator (see Section 6.3.4.5, "Customizing WCF
HTML Pages"). Note that the banner file is not displayed when a virus is detected in large files for
the first time.
Use of the Cache and Log Events
There are no additional log messages related to cache operation. The same virus_found log
message will be generated by NetDefendOS if an anti-virus scan has actually been done or if the
file URL was found in the cache. Cache usage is not indicated in the log events generated.
The Lifetime for Cache Entries
By default, an entry stays in the cache for a set period of time which is determined by the global
setting Anti-Virus Cache Lifetime. After the lifetime expires, the entry is removed from the cache
and a fresh anti-virus scan of the file is done by NetDefendOS if a new download is requested.
This means that if the problem with the file is fixed between the URL entering the cache and
being deleted from the cache (by default, the cache lifetime is 20 minutes) then the file will be
successfully downloaded on the next attempt.
The administrator may not have control over the file problem being rectified if it is located on the
public Internet. However, they may be able to fix the issue if the file is located on a local
webserver that might be located in a DMZ.
Example 6.30. Changing the Anti-Virus Cache Lifetime
This example changes the lifetime of an entry in the anti-virus cache to 15 minutes.
Command-Line Interface
gw-world:/> set Settings MiscSettings AVCache_Lifetime=15
Web Interface
1. Go to: System > Advanced Settings > Misc. Settings
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Chapter 6: Security Mechanisms