Keep in mind the following guidelines and limitations for application control:
Ensuring
that Adaptive Profiling is Enabled
If adaptive
profiling is not enabled (its default state), access control rules cannot
perform application control.
Automatically
Enabling Application Detectors
If no detector is enabled for an application you want to detect,
the system automatically enables all system-provided detectors for the
application. If none exist, the system enables the most recently modified
user-defined detector for the application.
Configure Your Policy to Examine the Packets That Must Pass Before an Application Is Identified
The system cannot perform application control, including Intelligent Application Bypass (IAB) and rate limiting, before both of the following occur:
This identification should occur in 3 to 5 packets, or after the server certificate exchange in the SSL handshake if the traffic
is encrypted.
Important! To ensure that your system examines these initial packets, see Specify a Policy to Handle Packets That Pass Before Traffic Identification.
If early traffic
matches all other criteria but application identification is incomplete, the
system allows the packet to pass and the connection to be established (or the
SSL handshake to complete). After the system completes its identification, the
system applies the appropriate action to the remaining session traffic.
Create Separate Rules for URL and Application Filtering
Create separate rules for URL and application filtering whenever possible, because combining application and URL criteria
can lead to unexpected results, especially for encrypted traffic.
Rules that include both application and URL criteria should come after application-only or URL-only rules, unless the application+URL
rule is acting as an exception to a more general application-only or URL-only rule.
URL Rules
Before Application and Other Rules
For the most
effective URL matching, place rules that include URL conditions before other
rules, particularly if the URL rules are block rules and the other rules meet
both of the following criteria:
Application
Control for Encrypted and Decrypted Traffic
The system can identify and filter encrypted and decrypted
traffic:
-
Encrypted
traffic—The system can detect application traffic encrypted with StartTLS,
including SMTPS, POPS, FTPS, TelnetS, and IMAPS. In addition, it can identify
certain encrypted applications based on the Server Name Indication in the TLS
ClientHello message, or the subject distinguished name value from the server
certificate. These applications are tagged
SSL Protocol; in an SSL rule, you can choose only
these applications. Applications without this tag can only be detected in
unencrypted or decrypted traffic.
-
Decrypted
traffic—The system assigns the
decrypted traffic tag to applications that the
system can detect in decrypted traffic only, not encrypted or unencrypted.
TLS Server Identity Discovery and Application Control
The latest version of the Transport Layer Security (TLS) protocol 1.3, defined by RFC 8446, is the preferred protocol for many web servers to provide secure communications. Because the TLS 1.3 protocol encrypts the
server's certificate for additional security, and the certificate is needed to match application and URL filtering criteria
in access control rules, the Firepower System provides a way to extract the server certificate without decrypting the entire packet.
We strongly recommend enabling it for any traffic you want to match on application or URL criteria, especially if you want
to perform deep inspection of that traffic. An SSL policy is not required because traffic is not decrypted in the process of extracting the server certificate.
For more information, see Access Control Policy Advanced Settings.
Exempting
Applications from Active Authorization
In an identity
policy, you can exempt certain applications from active authentication,
allowing traffic to continue to access control. These applications are tagged
User-Agent Exclusion. In an identity rule, you
can choose only these applications.
Handling
Application Traffic Packets Without Payloads
When performing access control, the system applies the default
policy action to packets that do not have a payload in a connection where an
application is identified.
Handling
Referred Application Traffic
To handle traffic referred by a web server, such as
advertisement traffic, match the referred application rather than the referring
application.
Controlling Application Traffic That Uses Multiple Protocols (Skype, Zoho)
Some applications use multiple protocols. To control their traffic, make sure your access control policy covers all relevant
options. For example:
-
Skype—To control Skype traffic, choose the Skype tag from the Application Filters list rather than selecting individual applications. This ensures that the system can detect and control all Skype traffic
the same way.
-
Zoho—To control Zoho mail, choose both
Zoho and Zoho mail from the Available Application list.
Search Engines
Supported for Content Restriction Features
The system
supports Safe Search filtering for specific search engines only. The system
assigns the
safesearch supported tag to application traffic
from these search engines.