What is the Smurf attack?

The Smurf attack is a Denial of Service or DoS attack, which can make a system inaccessible completely. In Smurf Attack, an attacker creates lots of ICMP packets with the target victim’s IP address as source IP and broadcasts those packets in a computer network using an IP broadcast address.

As a result, most devices of the network respond by sending a reply to the victim’s IP address. If the number of devices in the network is very large and most of the devices send a reply, the victim’s machine floods with network traffic. This can slow down the victim’s computer to such an extent that the target system will become completely inaccessible and result in a Denial of Service Attack.

How to prevent the Smurf attack?

There are three ways to prevent this attack:

• You can configure individual hosts and routers in the network not to respond to ICMP requests or broadcasts.
• You can configure routers not to forward packets directed to broadcast addresses.
• The third solution is ingress filtering. You can block the packets in the network that come from outside the network and have a source address that belongs to the network.

The Fraggle attack is also a variation of the Smurf attack. In this attack, the attacker sends a large number of UDP packets to ports 7 (echo) and 19 (Chargen or Character Generator). Attackers send those packets to an IP Broadcast address with the target victim’s IP address as the source IP address. The result is very similar to the Smurf attack.

Interested readers can find more information on how to protect servers from DDoS attacks here: How to protect your servers from DDoS attacks?

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