  Network intrusion detection systems play a critical role in protecting the
information infrastructure of an organization. Due to the sophistication and
complexity of techniques used for the analysis they are commonly based on
general-purpose workstations. Although cost-efficient, these general-purpose
systems are found to be inadequate as they are unable to perform efficiently at
high packet rates. The resulting packet loss degrades the system's overall
effectiveness, as the analyzing capability of the system is reduced. It has
been found that the performance of these sensors can be improved significantly
by filtering out unwanted packets. This paper presents the design of a
Programmable Ethernet Interface Card that is used to offload signature matching
from software and thereby improve the detection ratio and performance of the
system.
