The ICMP echo request and the ICMP echo reply messages are commonly known as ping messages. Ping is a troubleshooting tool used by system administrators to manually test for connectivity between network devices, and also to test for network delay and packet loss. The ping command sends an ICMP echo request to a device on the network, and the device immediately responds with an ICMP echo reply. Sometimes, a company's network security policy requires ping (ICMP echo reply) to be disabled on all devices to make them more difficult to be discovered by unauthorized persons.