An Intrusion Prevention System (IPS) is a component of network security that monitors, identifies, and ultimately takes action to protect the network, applications, and/or servers from web threats and vulnerability exploits. An IPS is an an additional layer of security that is placed in-line and can automatically take protective actions to mitigate harm from detected threats and attacks.
Traditional, hardware-based IPS systems typically sit behind the firewall, and monitor for vulnerability exploits, which look for and attempt to take advantage of unpatched operating systems and/or applications within the network. IPS systems typically scan the traffic immediately after the firewall, and usually prevent any exploit attempts before the traffic reaches the switch/router level. This is is an important layer of security, particularly for businesses that have challenges with security patching and/or a large amount of application sprawl. The more applications you have, the harder it is to keep security and maintenance patches up to date, and the more likely you are to fall victim to a vulnerability in your application or OS stack.
Unlike a related technology called an Intrusion Detection System (IDS) which simply detects and reports on threats, an IPS is meant to do what its name implies... prevent intrusions. This added layer of security works as a complement to other network security components.
A traditional intrusion prevention system does have it's limitations when it comes to protecting any threats to a network or system that's outside the network itself. The next generation intrusion prevention systems (NGIPS) are addressing this by basing IPS in the cloud rather than at the firewall level.
Traditionally IPS solutions are built to protect servers. Although protecting the server is vital, today's threats are more frequently targeting users directly and many threats are now coming via SSL encrypted traffic. Throw in the fact that apps are moving to the cloud, it's clear cloud based IPS will be the new normal to ensure users outside the network are protected and threats from outside the network are prevented.