Exercise granular policy control over applications to minimize the range of
unidentified traffic on your network, thereby reducing the attack surface.
To safely enable applications you must classify all traffic, across all ports, all
the time. With App-ID, the only applications that are typically classified as
unknown traffic—tcp, udp or non-syn-tcp—in the ACC and the Traffic logs are
commercially available applications that have not yet been added to App-ID, internal
or custom applications on your network, or potential threats.
To ensure that your internal custom applications don't show up as unknown traffic,
create a custom application. You can then exercise granular policy control over
these applications in order to minimize the range of unidentified traffic on your
network, thereby reducing the attack surface. Creating a custom application also
allows you to correctly identify the application in the ACC and Traffic logs, which
enables you to audit/report on the applications on your network.
To create a custom application, you must define the application attributes: its
characteristics, category, and sub-category, risk, port, timeout. In addition, you
must define patterns or values that the your configuration can use to match to the
traffic flows themselves (the
signature). Finally, you can attach the
custom application to a Security rule that allows or denies the application
(or add it to an application group or match it to an application filter). You can
also create custom applications to identify ephemeral applications with topical
interest, such as ESPN3-Video for world cup soccer or March Madness.
In order to collect the right data to create a custom application signature,
you'll need a good understanding of packet captures and how datagrams are
formed. If the signature is created too broadly, you might inadvertently include
other similar traffic; if it's defined too narrowly, the traffic will evade
detection if it does not strictly match the pattern.
Custom applications are stored in a separate database on the firewall and this
database isn't impacted by the weekly App-ID updates.
The supported application protocol decoders that enable the firewall to detect
applications that may be tunneling inside of the protocol include the following
as of content release version 609: FTP, HTTP, IMAP, POP3, SMB, and SMTP.
The following is a basic example of how to create a custom application.