A smurf attack is an exploitation of the Internet Protocol (IP) broadcast addressing to create a denial of service. The attacker uses a program called Smurf to cause the attacked part of a network to become inoperable. The exploit of smurfing, as it has come to be known, takes advantage of certain known characteristics of the Internet Protocol (IP) and the Internet Control Message Protocol (ICMP). The ICMP is used by network nodes and their administrators to exchange information about the state of the network. ICMP can be used to ping other nodes to see if they are operational. An operational node returns an echo message in response to a ping message.
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The smurf program builds a network packet that appears to originate from another address (this is known as spoofing an IP address). The packet contains an ICMP ping message that is addressed to an IP broadcast address, meaning all IP addresses in a given network. The echo responses to the ping message are sent back to the "victim" address. Enough pings and resultant echoes can flood the network making it unusable for real traffic.
One way to defeat smurfing is to disable IP broadcast addressing at each network router since it is seldom used. This is one of several suggestions provided by the CERT Coordination Center. The name of the exploit was inspired by a Belgian comic series that was popularized in the United States by Hannah-Barbera during the 1980's.