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Cisco ASA and PIX Firewall Handbook by Dave Hucaby

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6-4. Filtering Content

A firewall normally allows outbound HTTP or HTTPS connections to any URL, provided that the outbound access list permits the connection. An audit trail of URL activity is available only through the firewall Syslog records, using Syslog message 304001 at the default severity level, 5 (notifications).

Cisco firewalls can use third-party web content-filtering applications to enforce URL policies. These content filters run on a local server but download periodic updates of web content databases. Web content is categorized, and content rules can be applied to corporate users or groups of users.

When a user sends a URL request, the firewall relays the request to the content-filtering server. If the server determines that the ...

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