RangerIDS - Intrusion Detection System (IDS)



Gigabit IDS


Clearly, host-based IDS in their various forms are not (or should not be) affected by the speed of the network on which they are installed. Therefore whenever we talk about Gigabit IDS we are, by definition, focussing on Network IDS with a Gigabit capability.  


Where life gets difficult for those tasked with evaluating this technology is that different vendors have different ideas about what constitutes Gigabit IDS. Some products will be true Gigabit products, capable of pulling traffic off the wire for analysis at speeds of up to 1000Mbps (or beyond). Others are merely appliances that contain a Gigabit network card, whose main aim is to allow them to cope with 100Mbps or multiple 100Mbps segments easily.  


There is nothing inherently wrong with the latter approach providing the marketing message is honest and does not describe the product as a true Gigabit appliance. As long as all the customer needs is to be able to handle 100-200Mbps with confidence - and the price is right, of course - then this is a perfectly valid tactic. 


Even true wire-speed Gigabit appliances will have problems in certain areas if they are assembled from off-the-shelf components. At the time of writing, not even the best Gigabit network cards on the market are capable of pulling almost 1.5 million packets per second off the wire, never mind analysing that level of traffic. Thus a Gigabit network loaded with small packets (64 bytes) will cause problems for most Gigabit solutions, and the only way around that for the time being is to move towards custom hardware and ASICs.  


Administrators need to be aware of the overall performance limitations of any device when deploying on Gigabit networks. As with most Fast Ethernet networks, the average Gigabit subnet is unlikely to see much more than a fraction of its total available bandwidth in use at any given point in time, and so where only 200-400Mbps is being used, the performance of the Gigabit IDS used to monitor it is less of an issue.  


However, one tactic being employed in some organizations is to consolidate multiple 100Mbit segments using a Gigabit switch, and copy all the traffic from each segment to a single mirror, or SPAN (Switched Port ANalyser) port. The Gigabit IDS sensor is then attached to this port to monitor all of the traffic across multiple subnets, thus providing a cost-effective solution to monitoring a number of subnets using a single sensor.  


Of course, even if the average utilisation of each subnet is only 40-50Mbps, once you mirror 20 of these you are asking your IDS sensor to monitor getting on for a full Gigabit of network traffic (providing your switch is actually capable of mirroring that amount of traffic, of course - an entire topic in itself which is beyond the scope of this report). This is when the performance limitations of some so-called Gigabit devices will begin to manifest themselves. 


In some respects, detection performance is the least of the problems facing the administrator tasked with deploying these devices. The problem with any Gigabit IDS product is, by its very nature and capabilities, the amount of alert data it is likely to generate. With 1Gbps of traffic passing through the IDS, the number of alerts could reasonably be expected to be ten times that generated by the typical 100Mbps product. How many members of staff would be needed to process, investigate and resolve that number of alerts? How long before the IDS becomes just another device in the corner that is largely ignored thanks to its insistence on overloading the administrator on a daily basis? 


More than ever before in the IDS space, centralised management reporting and forensic analysis is key to the success of the Gigabit IDS appliance. A reduction in false positives (through more accurate protocol decodes and signatures) and global pre-filtering of “safe” alerts that can be ignored are both essential. After that comes the ability to consolidate alerts from multiple sensors to a single management console. Far from increasing the load for a single administrator, this consolidation should help in identifying where potential break-ins are disguised by multiple exploits run over multiple subnets and over a long period of time.  


Some management solutions will leave the administrator to determine the connection between exploits, providing the tools to “slice and dice” the data in a myriad of different ways in order to achieve this, While others will attempt to perform the correlation in an automated fashion (with varying degrees of success). Either way, the ability to create high-level reports of activity over a period of time, reshuffle and resort alerts in different ways, and then drill down to discover the exact trigger that caused the alert in each case in an efficient manner is now essential. 


Without effective management capabilities, alert handling, and forensic analysis tools, the Gigabit IDS is just another lump of iron sitting in the machine room equipment rack.