What is a smurf DoS attack?

In a smurf DoS attack, an attacker sends a large amount of ICMP echo request traffic to the IP broadcast addresses. These ICMP requests have a spoofed source address of the intended victim. If the routing device delivering traffic to those broadcast addresses delivers the IP broadcast to all the hosts, most of the IP addresses send an ECHO reply message. However, on a multi-access broadcast network, hundreds of computers might reply to each packet when the target network is overwhelmed by all the messages sent simultaneously. Due to this, the network becomes unable to provide services to all the messages and crashes.