Enable Logging to Obtain Traffic Statistics
You can monitor a wide range of traffic statistics using the monitoring dashboards and the Event Viewer. However, you must enable logging to tell the system which statistics to collect. Logging generates various types of events that provide insight into the connections going through the system.
The following topics explain more about events and the information they provide, with special emphasis on connection logging.
The system can generate the following types of events. You must generate these events to see related statistics in the monitoring dashboards.
- Connection Events
You can generate events for connections as users generate traffic that passes through the system. Enable connection logging on access rules to generate these events. You can also enable logging on Security Intelligence policies and SSL decryption rules to generate connection events.
Connection events include a wide variety of information about a connection, including source and destination IP addresses and ports, URLs and applications used, and the number of bytes or packets transmitted. The information also includes the action taken (for example, allowing or blocking the connection), and the policies applied to the connection.
- Intrusion Events
The system examines the packets that traverse your network for malicious activity that could affect the availability, integrity, and confidentiality of a host and its data. When the system identifies a possible intrusion, it generates an intrusion event, which is a record of the date, time, type of exploit, and contextual information about the source of the attack and its target. Intrusion events are generated for any intrusion rule set to block or alert, regardless of the logging configuration of the invoking access control rule.
- File Events
File events represent files that the system detected, and optionally blocked, in network traffic based on your file policies. You must enable file logging on the access rule that applies the file policy to generate these events.
When the system generates a file event, the system also logs the end of the associated connection regardless of the logging configuration of the invoking access control rule.
- Malware Events
The system can detect malware in network traffic as part of your overall access control configuration. AMP for Firepower can generate a malware event, containing the disposition of the resulting event, and contextual data about how, where, and when the malware was detected. You must enable file logging on the access rule that applies the file policy to generate these events.
The disposition of a file can change, for example, from clean to malware or from malware to clean. If AMP for Firepower queries the AMP cloud about a file, and the cloud determines the disposition has changed within a week of the query, the system generates retrospective malware events.
- Security Intelligence Events
Security Intelligence events are a type of connection event generated by the Security Intelligence policy for each connection blocked or monitored by the policy. All Security Intelligence events have a populated Security Intelligence Category field.
For each of these events, there is a corresponding “regular” connection event. Because the Security Intelligence policy is evaluated before many other security policies, including access control, when a connection is blocked by Security Intelligence, the resulting event does not contain the information that the system would have gathered from subsequent evaluation, for example, user identity.
Configurable Connection Logging
You should log connections according to the security and compliance needs of your organization. If your goal is to limit the number of events you generate and improve performance, only enable logging for the connections critical to your analysis. However, if you want a broad view of your network traffic for profiling purposes, you can enable logging for additional connections.
Because the system can log a connection for multiple reasons, disabling logging in one place does not ensure that matching connections will not be logged.
You can configure connection logging in the following places.
Access control rules and default action—Logging at the end of a connection provides the most information about the connection. You can also log the beginning of the connection, but these events have incomplete information. Connection logging is disabled by default, so you must enable it for each rule (and the default action) that targets traffic that you want to track.
Security Intelligence policy—You can enable logging to generate Security Intelligence connection events for each blocked connection. When the system logs a connection event as the result of Security Intelligence filtering, it also logs a matching Security Intelligence event, which is a special kind of connection event that you can view and analyze separately.
SSL Decryption rules and default action—You can configure logging at the end of a connection. For blocked connections, the system immediately ends the session and generates an event. For monitored connections and connections that you pass to access control rules, the system generates an event when the session ends.
Automatic Connection Logging
The system automatically saves the following end-of-connection events, regardless of any other logging configurations.
The system automatically logs connections associated with intrusion events, unless the connection is handled by the access control policy's default action. You must enable logging on the default action to get intrusion events for matching traffic.
The system automatically logs connections associated with file and malware events. This is for connection events only: you can optionally disable the generation of file and malware events.
Tips for Connection Logging
Keep the following tips in mind when considering your logging configuration and the evaluation of related statistics:
When you allow traffic with an access control rule, you can use an associated intrusion or file policy (or both) to further inspect traffic and block intrusions, prohibited files, and malware before the traffic can reach its final destination. Note, however, that by default file and intrusion inspection is disabled for encrypted payloads. If the intrusion or file policies find reason to block a connection, the system immediately logs an end-of-connection event regardless of your connection log settings. Logging allowed connections provides the most statistical information on the traffic in your network.
A trusted connection is one that is handled by a Trust access control rule or the default action in an access control policy. However, trusted connections are not inspected for discovery data, intrusions, or prohibited files and malware. Therefore, connection events for trusted connections contain limited information.
For access control rules and access control policy default actions that block traffic, the system logs beginning-of-connection events. Matching traffic is denied without further inspection.
Logging blocked TCP connections during a Denial of Service (DoS) attack can affect system performance and overwhelm the database with multiple similar events. Before you enable logging for a Block rule, consider whether the rule monitors traffic on an Internet-facing interface or other interface vulnerable to DoS attack.
Sending Events to an External Syslog Server
Besides viewing events through Firepower Device Manager, which has a limited capacity to store events, you can selectively configure rules and policies to send events to an external syslog server. You can then use the features and additional storage of your selected syslog server platform to view and analyze event data.
To send events to an external syslog server, edit each rule, default action, or policy that enables connection logging and select a syslog server object in the log settings. To send intrusion events to a syslog server, configure the server in the intrusion policy settings.
For more information, see the help for each rule and policy type and also see Configuring Syslog Servers.