MAC flooding

In computer networking, MAC flooding is a technique employed to compromise the security of network switches.

Switches maintain a MAC Table that maps individual MAC addresses on the network to the physical ports on the switch. This allows the switch to direct data out of the physical port where the recipient is located, as opposed to indiscriminately broadcasting the data out of all ports as a hub does. The advantage of this method is that data is bridged exclusively to the network segment containing the computer that the data is specifically destined for.

In a typical MAC flooding attack, a switch is fed many Ethernet frames, each containing different source MAC addresses, by the attacker. The intention is to consume the limited memory set aside in the switch to store the MAC address table.

The effect of this attack may vary across implementations, however the desired effect (by the attacker) is to force legitimate MAC addresses out of the MAC address table, causing significant quantities of incoming frames to be flooded out on all ports. It is from this flooding behavior that the MAC flooding attack gets its name, and it is this behavior which allows the MAC flooding attack to be used as more than a simple denial-of-service attack against the switching infrastructure.