One of the many tools for sniffing traffic and gathering statistics is ntop. You can download it from www.ntop.org or use a package manager on your system to install it. There already are cooked packages for popular Linux distributions, such as Red Hat, Debian/Ubuntu and SUSE. Before using it, you have to set up an admin password by running the following:
sudo ntop --set-admin-password
And start it with:
sudo /etc/init.d/ntop start
Now you can go to your IP address (http://127.0.0.1:300) and look for some statistics. This is a very powerful tool that provides a lot of information. You can sort by packets, ports, hosts and so on. Network usage graphs also are helpful in determining the amount of traffic getting into your system.
Remember, no packets should be legitimate in Darknet, so this tool provides great statistical data as to what hosts/networks are responsible for illegal traffic.
Figure 5 shows ntop's graphic interface and its ability to detect host operating systems, vendor and other details in Host view.
Figure 6 presents standard ntop graph capabilities, thanks to built-in support for RRDTool.
To get alerts regarding what exploits are used (if any) on your network, you need a network IDS system. The best one that's publicly available is Snort. You can get it from www.snort.org, and it also is available on many systems as a binary package.
One thing you need to configure in /etc/snort/snort.conf is setting your $HOME_NETWORK variable to match IP addresses and netmask to your configuration. Snort is an intrusion detection system based on a pattern database.
If traffic matches, it will write an alert to a log file (by default in /var/log/snort) and record the packets for later analysis (you can reply to them using the tcpdump -r command or examine them using tools like Wireshark).
With powerful yet not complicated rules, you can write your own signatures or edit existing ones to record traffic that matches your custom criteria. Additionally, you can consider installing Snort support tools, such as IDScenter (see Resources).
There also is a Honeynet project, based on Snort and Sebek technologies. It provides a cut-down Linux system, based on Fedora and custom-built tools with a GUI for incident management (Figure 7).
If you want to go further, there also are projects, such as HIHAT (Highly Interactive Honeypot Analyses Toolkit), that transform popular PHP applications, such as PHPNuke or osCommerce, to fully functional logging, reporting and alerting tools.
You easily can detect commands and SQL injections, cross-site scripting and map involved IPs to geographic locations, as shown in Figure 8.
This simple configuration of putting a server on an internal Darknet allows us to detect and receive alerts on the following:
Actively spreading malware.
Covert channels and possible data leakage.
Suspicious activities (deliberate or not), such as abuse of a company's policy and network reconnaissance attempts (for example, port scanning).
Provide audit trails and record evidence for later investigation.
Provide general network usage statistics for base-lining.