Scapy is a tool that can be used to craft and inject custom packets into a network. In this specific recipe, Scapy will be used to scan for active UDP services. This can be done by sending an empty UDP packet to destination ports and then identifying the ports that do not respond with an ICMP port-unreachable response.
To use Scapy to perform UDP scanning, you will need to have a remote system that is running network services over UDP. In the examples provided, an instance of Metasploitable2 is used to perform this task. For more information on how to set up Metasploitable2, refer to the Installing Metasploitable2 recipe in Chapter 1, Getting Started. Additionally, this section will require a script to be written to the filesystem using a text editor, such as VIM or Nano. For more information on how to write scripts, refer to the Using text editors (VIM and Nano) recipe in Chapter 1, Getting Started.