For security reasons, many organizations do not allow error reply messages to leave their internal Internets. How, specifically, could hackers use information in echo reply messages to learn about the firm's internal hosts? Does the same thing apply to ping requests?
ICMP was designed to help determine characteristics of the network. PING is an application of ICMP.
ICMP has two modes of operation:
The errors are produced in special conditions such as:
By using ICMP messages and errors it is possible to gather substantial information about the network:
ICMP error messages are not typically involved in directly attacking the network but would greatly help an attacker understand more about the network and know how and where to attack. Therefore this information should not leave the network because it should not be available to people outside the network.