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2.2. Events and Logging
2.2.1. Overview
The ability to log and analyze system activities is an essential feature of NetDefendOS. Logging
enables not only monitoring of system status and health, but also allows auditing of network usage
and assists in trouble-shooting.
NetDefendOS defines a number of event messages, which are generated as a result of corresponding
system events. Examples of such events are the establishment and teardown of connections, receipt
of malformed packets as well as the dropping of traffic according to filtering policies.
Whenever an event message is generated, it can be filtered and distributed to all configured Event
Receivers. Multiple event receivers can be configured by the administrator, with each event receiver
having its own customizable event filter.
2.2.2. Event Messages
NetDefendOS defines several hundred events for which event messages can be generated. The
events range from high-level, customizable, user events down to low-level and mandatory system
events.
The conn_open event, for example, is a typical high-level event that generates an event message
whenever a new connection is established, given that the matching security policy rule has defined
that event messages should be generated for that connection.
An example of a low-level event would be the startup_normal event, which generates a mandatory
event message as soon as the system starts up.
All event messages have a common format, with attributes that include category, severity and
recommended actions. These attributes enable easy filtering of messages, either within
NetDefendOS prior to sending to an event receiver, or as part of the analysis after logging and
storing messages on an external log server.
A list of all event messages can be found in the NetDefendOS Log Reference Guide. That guide also
describes the design of event messages, the meaning of severity levels and the various attributes
available. The severity of each event is predefined and it can be, in order of severity, one of:
Emergency
Alert
Critical
Error
Warning
Notice
Info
Debug
By default all messages of level Info and above are sent. The Debug category of designed for
troubleshooting only and should only be turned on if required to try and solve a problem. Messages
of all severity levels are found listed in the NetDefendOS Log Reference Guide.
2.2.3. Event Message Distribution
To distribute and log the event messages generated, it is necessary to define one or more event
receivers that specify what events to capture, and where to send them.
NetDefendOS can distribute event messages in the following ways:
Memlog NetDefendOS has a built in logging mechanism known as the Memory Log. This retains
all event log messages in memory and allows direct viewing of log messages through the
2.2. Events and Logging Chapter 2. Management and Maintenance
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