Related to firewalls are systems known as intrusion detection systems
(IDS) and intrusion prevention systems (IPS). These systems try to look
for anomalous activity, such as an unusually large amount of traffic targeting
a given host or port number, for example, and generate alarms for
network managers or perhaps even take direct action to limit a possible
attack. While there are commercial products in this space today, it is still
a developing field.