Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP)
ICMP works at the Network layer and provides the functions used for Network layer management and control. Routers send ICMP messages to respond to undeliverable datagrams by placing
an ICMP message in an IP datagram and then sending the datagram back to the original source. The ping command—used in network troubleshooting and described in Chapter 5,
“Major Network Operating Systems”—uses ICMP.