Logging and Log-Analysis Tools
| Most firewalls can log events related to traffic that has been permitted or denied. Unfortunately, the sheer volume of data from even a moderately sized environment can quickly become unmanageable. Most firewalls use one of two types of logging methods:
Syslog requires a server and a client component. The client typically runs on the firewall itself; the server is installed on a Windows, Linux, or UNIX host. Syslog server functionality on Linux and UNIX is built in to the operating system. For Windows hosts, however, you must install a third-party syslog server. A popular Windows-based syslog server is the Kiwi Syslog Daemon available at http://www.kiwisyslog.com/. Kiwi Syslog allows not only for the logging of events from the firewall but also provides advanced functionality such as implementing hashing on the logs for chain of custody and legal reasons, event filtering, and event notification via e-mail and pager for specified events. Syslog uses a combination of facilities and severities to identify the source and type of message that is being generated. Although there are 24 total facilities, most firewalls are configured to use facilities local0 to local7. Message severity consists of the following severity levels:
In most cases, you should log debug-level severity messages only for the purposes of troubleshooting. A good default setting is to log all messages between Emergency and Informational level and then reduce the information logged accordingly after you have established what information you can obtain from more restrictive logging levels (that is, Notice or Warning). In the case of the Cisco Secure PIX Firewall, configuring the firewall to log to a syslog server is a relatively trivial task. Example A-8 shows a sample of the commands to be executed. Example A-8. Configuring a Cisco Secure PIX Firewall to Use Syslog
A valuable component of logging events is the ability to perform log analysis. Whereas most syslog servers enable you to log events, few enable you to perform event correlation or event analysis. In addition, it quickly becomes an insurmountable task for a human being to review the logs in a timely fashion to identify security events or negative trends. Therefore, it is typically necessary to implement a complex scripting environment to parse and correlate the logs that are collected or to use third-party log-analysis tools such as Cisco Security Monitoring, Analysis, and Response System (CS-MARS), Net IQ Security Manager, LogLogic, Network Intelligence, and SenSage. These tools all provide for the archival, parsing, and reporting of huge amounts of data, shifting the burden from the security staff and firewall admins to an automated and intelligent system of review and notification. |
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