Whenever a company connects its network to the Internet, it opens up a whole can of worms regarding security. As the network grows, it will play host to numerous bugs and security loop holes of which you have never heard - but you can bet intruders have.

Many organisations are recognising the value of a good security policy to define what is and is not allowed in terms of network and Internet access. Then they deploy a number of tools to enforce that security policy – usually in the form of a firewall or two.

Firewalls may be billed as commodity items, but the “shrink wrap” element certainly doesn’t extend to their configuration. A detailed knowledge of what a hacker can do and what should and shouldn’t be allowed through the firewall is required before embarking on the configuration adventure, and a slip of the mouse is all it takes to open up a hole big enough for your average hacker to drive the proverbial bus through. The problem is, a badly configured firewall can be worse than no firewall at all, since it will engender a false sense of security.

To protect an organisation completely, therefore, it is necessary to provide a second line of defence, and in order to achieve this, an entire category of software exists in the form of Intrusion Detection Systems (IDS).

When it comes to computer and network security, there are a number of analogies that can be drawn with the “real world”. Such analogies are particularly useful for answering such questions as “I already have a firewall, why do I need Intrusion Detection Systems as well?”.

Depending on how you approach the security of your home, for example, you may opt for high quality locks on your doors and windows. That will help to keep intruders out, and could be thought of as the equivalent of the firewall – perimeter defences. It’s nice to feel secure, but the determined burglar can often find ways around these measures. He can always throw a brick through your back window, for instance, and get in that way – or perhaps you simply forget to lock your door one day.

Once he is inside your home he is free to wreak havoc, perhaps making it obvious he has been there by stealing or wrecking things, or perhaps simply taking copies of any keys he finds so he can come and go later at his leisure. Whatever happens, you don’t want your first knowledge of the break-in to be when you return home to the ransacked contents.

That is why many people install a burglar alarm as well. Should the intruder gain access through the perimeter defences, the burglar alarm alerts you or your neighbours to the break in immediately, and provides an additional deterrent to the would-be thieves.

IDS, therefore, are the equivalent of the burglar alarm. To be used alongside firewalls, they are a recognition of the fact that you can never have a 100 per cent secure system. However, should someone be clever enough to breach your perimeter defences, you want to know about it as soon as possible.

It would also be nice to know what they have been up to while they were inside too.

Intrusion Detection and Vulnerability Assessment are becoming increasingly important as the stakes become higher. In the 1980s and early 1990s, denial-of-service (DoS) attacks were infrequent and not considered serious. Today, successful DoS attacks can shut down e-commerce-based organisations like online stockbrokers and retail sites.

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 1,000Mbps (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.

To read the rest of this comprehensive and independent report on Gigabit IDS, and the version examining 100Mbps IDS, please visit the links at the bottom of this page. The full reports can be downloaded in PDF format and are 168 and 143 pages respectively.

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