As a first line of defense against malicious Internet content, the Firepower System includes the Security
Intelligence feature, which allows you to immediately blacklist (block) connections based on the latest
reputation intelligence, removing the need for a more resource-intensive, in-depth analysis.
Security Intelligence works by blocking traffic to or from IP addresses, URLs, or domain names that have a
known bad reputation. This traffic filtering takes place before any other policy-based inspection, analysis, or
traffic handling (although it does occur after hardware-level handling, such as fast-pathing).
Note that you could create access control rules that perform a similar function to Security Intelligence filtering
by manually restricting traffic by IP address or URL. However, access control rules are wider in scope, more
complex to configure, and cannot automatically update using dynamic feeds.
Traffic blacklisted by Security Intelligence is immediately blocked and therefore is not subject to any further
inspection—not for intrusions, exploits, malware, and so on, but also not for network discovery. You can
override blacklisting with whitelisting to force access control rule evaluation, and, recommended in passive
deployments, you can use a “monitor-only” setting for Security Intelligence filtering. This allows the system
to analyze connections that would have been blacklisted, but also logs the match to the blacklist and generates
an end-of-connection security intelligence event.
➥ Procedure to block some websites:
#1) In the Access Control Policy editor, click the Security Intelligence tab;
#2) Click the URLs tab to add New URL list;
#3) Change the Type box to "List", import your .txt file and upload it;
#4) Now you can deploy and test.