A baseline of network operations and expected data flows for users and systems is established and managed.

The organization maintains documentation of interfaces and other connections between data system and the data transmission methods used in the interfaces.

The documentation concerning the interfaces shall be reviewed regularly and after significant changes to data systems.

Normal network traffic is described and the description maintained to detect anomalies. The description should be updated:

• At intervals specified by the organization
• When necessary according to the situations defined by the organization
• When there are changes to the systems

Organization must describe the baseline of normal behaviour for the use of network and data systems, which is used as a starting point for identifying anomalies.

When defining the baseline, the following must be taken into account:

• monitoring the use of data systems during both normal and peak times
• usual times of use, places of use and frequency of use for each user and user group

Monitoring systems must be configured against the baseline to identify anomalous behavior such as:

• unplanned termination of systems or processes
• traffic related to malware or malicious IP addresses or domains
• known attack characteristics (e.g. denial of service or buffer overflow)
• unusual system use (e.g. keystroke logging)
• bottlenecks and overloads (e.g. network queues, latency levels)
• unauthorized access (actual or attempted) to systems or data
• unauthorized scanning of data systems and networks
• successful and failed attempts to access protected resources (e.g. DNS servers, web portals and file systems)
• unusual user and system behavior

System logs often contain a wealth of information, much of which is irrelevant to security monitoring. In order to identify events relevant to security monitoring, consideration should be given to automatically copying appropriate message types to another log or to using appropriate utilities or audit tools to review and resolve files.