Uncomplicated Firewall (UFW) is the default IPv4 or IPv6 host-based firewall that comes preinstalled with Ubuntu. This firewall is a layer of security that designates what traffic is and isn't allowed to enter the computer network. This firewall filters through network packets for malicious code and attack vectors that have been established as threats. The UFW also has a built-in intrusion detection system that will help catch threats before they can access our VM.

Snort is an open-source network intrusion detection system, which is available for Linux, Unix and Windows operating systems. First released in 1998, this system is considered the most popular with a large community following. This system can perform numerous functions such as packet lagging on IP networks, real time traffic analysis, content searching and matching, as well as being used for detecting various attacks and probes.

Snort works by monitoring network traffic in real time. The system closely inspects each packet and matches them with predefined rules to detect any dangerous or suspicious activity. If any suspicious behavior is discovered, an alert is created and logged to an alert file.

Nagios Core with its available plugins are an open-source network monitoring solution originally written for Linux. Its purpose is to monitor the connected nodes in the network, from switches to complete workstations. The monitoring ensures that the systems, applications, services, and the related business processes are functioning properly.