ICMP supports IP to help ensure data delivery; however, it can also be used in malicious ways. For example, ICMP can be used to conduct reconnaissance as a precursor to an attack, or even to help evade firewall rules. In this section, we'll provide an example of how ICMP can be used to obtain information on the network. Then, we'll evaluate some of the firewall rules. 

First, let's start with an overview of a ping sweep, which is used to see which network hosts might be awake.