Learn in the textbookFundamentals of Access Control and Network Defense Devices
DefinitionAn IPS (intrusion prevention system) spots signs of attack just as an IDS does, and then automatically blocks that traffic.
ExplanationAn IPS sits in the path of traffic and stops anything it judges to be an attack on the spot, so it limits damage without waiting for a person to act. On the other hand, if it mistakes normal traffic for an attack, it also blocks traffic the business needs.
AnalogyLike a shop security system that drops the shutter automatically when it senses a break-in. It does more than notice: it seals the entrance there and then.
Memory hookP is for Prevention. IDS and IPS differ by one letter, D versus P, and that letter tells you whether it reports or stops.