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Network Security Alchemy

Defining achievable IDS/IPS deployment goals

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A network intrusion detection (and prevention) system is a flexible tool that can be used in many different ways. Let’s outline some of the most common deployment types I see in use today on *real* networks, and look them in no particular order. The reason for looking at these deployment type is to encourage more common compartmentalization (or segmentation) of monitoring tasks.

Firstly let’s don’t not forget that I[DP]S is all about access controls, which controls are implemented are your choice.

a) Tactical threat suppression
b) Business link risk mitigation
c) Security event detection
d) Network audit controls

Tactical threat suppression (Provides a preventative access control)
This is normally seen as the deployment of IPS at key access gateways of a protected network, the policy deployed is set to prevent specific malicious traffic flows from gaining entry. This design meets the “virtual patch” ideas to protect assets from key threats that concern the security team. Think “sploit de jour”.

Security event detection (Provides a detective access control)
Deployment of an IDS to detect network events that could impact the traditional security goals of the network (think network security 101 goals here (C, I & A)).
This is probably the most commonly planned IDS deployment from the out-set, it defines a system that is inspects network data flow, and when a security event occurs a team of analysts is there do their “job”. Following analysis, some form of incident response policy would be followed that should lead to the event being resolved. The main requirement for this type operation is a tuned IDS system to detect events that matter to the organization where something can be done in response to them.

Business link risk mitigation (Provides a preventative access control)
The use of an IPS can decrease the risk associated with a network link, therefore allowing the organization to potentially conduct business with higher risk 3rd party networks. The IPS policy acts as a traffic scrubber to prevent potentially harmful flows from entering the network from less-trusted parties.

Network event recording (Provides an audit control)
Deployment of an IDS that monitors the network for potential security events and supporting information. This is sometimes seen as a failed “Security Event Detection” deployment, where an IDS just logs event data but isn’t inspected by an analyst in anything close to real-time. A report may be run once in a while, but the data is stored for future reference should it be needed.
I see this is as a very valid deployment goal, and those who want “all rules enabled” generally fit into this category.

Problems can appear when designs attempt mix requirements between these achievable goals, for example:

Security event detection + Network event recording:

This combination leads to access and audit controls being enabled in the same policy. Those who are interested in audit requirements commonly want “all rules enabled” and therefore create an un-tunable policy that cannot hope to provide accurate security event detection (read bucket loads of F+).

The methods used to analyze, store, and work with event data may vary across the deployment goals. For example, if a user wants to place a device outside of a firewall to provide audit records, keeping event data in a live event analysis system may be overkill. Maybe a better solution would be an event feed to a SAN in a flat-file system. This would remove the burden to keep event data in an analysis database for real-time access.

Splitting an IDS/IPS deployment into logical chunks, each with specific requirements makes makes a far more manageable and valuable deployment as these goals can be segmented and managed on their own. When I get time I will put more effort into explaining my ideas around this, but in the short term I wanted to throw some ideas out there.

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Written by leonward

July 8, 2008 at 6:12 pm

Posted in Security

Tagged with ,

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