The performance of a NIDS can be described by its ability to detect true attacks in the stream of network traffic it observes. In addition to the sophistication of the intrusion detection algorithm employed, processing speed is a key consideration for the overall performance. If the NIDS is unable to process network traffic at the rate it arrives, packets are dropped and valuable information may be lost. Significant packet loss negatively affects the overall NIDS effectiveness.
The performance requirements of the popular Snort NIDS has been studied before. However, in addition to the performance of the NIDS sensor itself, the database that receives and stores alerts can play a role in determining overall performance. On a system under attack, the NIDS sensor can potentially generate a large number of alerts over a short period of time. If the database server is unable to absorb alerts at the offered rate, important alert data is lost and the entire intrusion detection system is rendered inefficient. This problem is compounded if multiple NIDS sensors report to the same database system.
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