How can you use Snort for automated DDoS detection?

1 What is Snort?

Snort is a software that monitors your network traffic and analyzes it for signs of malicious activity, such as hackers, viruses, worms, or DDoS attacks. Snort can run in different modes, such as sniffer, packet logger, or network intrusion detection system (NIDS). In NIDS mode, Snort uses a set of rules to match the traffic patterns with known attack signatures, and generate alerts or take actions accordingly. Snort can also be integrated with other tools, such as databases, web interfaces, or firewalls, to enhance its functionality and performance.

2 How to install Snort?

To install Snort on your Linux system, you can use the package manager of your distribution, such as apt, yum, or zypper. Alternatively, you can download the source code from the official website and compile it yourself. You will also need to install some dependencies, such as libpcap, pcre, openssl, and zlib. After installing Snort, you will need to configure it according to your network environment and security needs. You can edit the snort.conf file in the /etc/snort/ directory, or use a graphical tool, such as SnortGUI or BASE, to manage your settings.

3 How to write Snort rules?

Snort rules are the core of its detection and prevention capabilities. They define the criteria that Snort uses to identify and react to suspicious or malicious traffic. A Snort rule consists of two parts: a rule header and a rule options. The rule header specifies the action, protocol, source and destination addresses and ports, and the direction of the traffic. The rule options provide more details about the content, metadata, or references of the traffic. For example, a simple rule to detect a SYN flood attack could look like this: alert tcp any any -> any 80 (flags: S; threshold: type both, track by_src, count 10, seconds 1; sid: 1001;) This rule tells Snort to alert on any TCP traffic from any source address and port to any destination address on port 80, with the SYN flag set, if it exceeds 10 packets per second from the same source. The rule also assigns a unique identifier (sid) to the rule, which can be used for reference or logging purposes.

4 How to configure Snort alerts?

Snort alerts are the notifications that Snort generates when it detects a match with a rule. Snort can produce alerts in different formats and destinations, such as console, syslog, file, database, or email. You can configure the alert mode and output in the snort.conf file, by using the -A and -l options, respectively. For example, to enable fast alert mode, which writes a single line for each alert, and send the alerts to a file named ddos.log in the /var/log/snort/ directory, you can use the following options: -A fast -l /var/log/snort/ You can also customize the alert format and content, by using the output or alert options in the snort.conf file, or by creating your own alert plugins.

5 How to automate Snort actions?

Snort actions are the responses that Snort takes when it detects a match with a rule. Snort can perform different actions, such as alert, log, pass, drop, reject, or sdrop. You can specify the action in the rule header, or use the default action of alert. For example, to drop the packets that match the SYN flood rule, you can change the action from alert to drop: drop tcp any any -> any 80 (flags: S; threshold: type both, track by_src, count 10, seconds 1; sid: 1001;) However, to enable Snort to drop or reject packets, you need to run it in inline mode, which requires a special configuration of your network interface card (NIC) or firewall. You can also use external tools, such as SnortSam or Guardian, to automate the firewall updates based on Snort alerts. For example, you can use SnortSam to block the source IP addresses of the DDoS attackers for a certain period of time, by adding the following option to the SYN flood rule: react: block; duration 3600; This option tells SnortSam to block the source IP address for one hour (3600 seconds) when the rule is triggered.

6 Here’s what else to consider

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