Understanding IDS, IPS and Software based UTM devices

There is always a confusion over IDS and IPS, how they are like or unlike UTM software modules. Everybody likes simple descriptive definition: so lets understand IDS, IPS and UTM in a simplistic way.

IDS

An Intrusion Detection Sensor (IDS) is a tool that most obviously detects things, but what things? Ultimately it could be anything. What’s unusual? In the simplest terms, it’s traffic you don’t want on your network, whether that is policy/misuse (IM, games, etc.) or the latest malware.

Monitoring traffic at the ingress/egress point will show you what comes and goes (after the firewall policy approves of course), but may not allow you to see remote offices connecting to core components

Monitoring all of the traffic on an internal switch, like your LAN or a DMZ, will allow the IDS to monitor user activity or key servers, but it won’t see things happening on other parts of the network. Unless you have unlimited resources, you may not be able to monitor everything on the network, so a key decision will be which traffic matters the most and which segment provides the best vantage point.

IDS can passively monitor more than one segment and can monitor traffic that an IPS or UTM would never see, such as the traffic staying entirely within a LAN or DMZ. An IDS, therefore, could alert on a desktop machine attacking other desktop machines on the LAN, something the IPS or UTM would miss due to being inline.

IPS

IPS and UTM, by their nature, must be inline and therefore can only see traffic entering and leaving an area. A huge concern is that an IPS can prevent business legitimate or revenue-generating traffic from occurring. IPS actions include drop, reset, shun or custom-scripted actions and all of this occurs immediately upon signature match. This potentially negative action makes the person responsible for security now responsible for loss in revenue should the IPS drop legitimate traffic. In my experience, IPS devices make great tools as long as you also leverage the key components that differentiate the IPS.

Also realize that only a small portion of the signatures that fire should actually be allowed to take action on traffic. To help reduce false positive rates, one should have very well defined home net or protected ranges allowing direction oriented signatures to be more effective. You will also need to spend quite a bit of time reviewing alarm and event output to ensure the signatures allowed to take action are working as intended. You can expect to spend more time up front and more time at each signature update looking at which signatures the vendor has chosen to take action and considering how that can impact your traffic. This often works best in settings where firewalls are not very favorably looked upon between “open” network segments.

Software based modules in UTM devices

Key items to point out about these devices happen to be drawbacks, though this does not reduce their efficacy. Obviously they can only be located where the UTM itself is located. Typically this is a junction point like your Internet gateway or an access control point between your LAN and DMZ. In this case a UTM would not be able to see all of the system-to-system traffic on the DMZ or LAN, rather only traffic coming and going from that segment.

In addition, UTMs are not purpose-built platforms, thus tending to have higher false positive rates.  In the case of high CPU or memory utilization, they will turn off software modules to preserve the primary function of the device, as a firewall.

Summary

None of the three are “set it and forget it” devices. New malware and vectors for exploit and detection emerge daily. Regardless of your choice, you will have often recurring maintenance in signature event/alarm output and a need to update and manage your policies, especially in the case of IPS. Updates can be automatically applied in any of the devices discussed, but that does not absolve the need for human review. Set aside some time daily to check in on your device and consider turning off groups of signatures that have no role in your environment (think “policy based”) and tuning out other noise granularly

Source: Alianvault