MAC flooding

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

Switches maintain a list (called a translation table) that maps individual MAC addresses on the network to the physical ports on the switch. This enables it to only send data out of the physical port where the recipient computer is located, instead of indiscriminately broadcasting the data out of all ports like a hub. The advantage of this method is that data is only routed to the computer that the data is specifically destined for.

In a typical MAC flooding attack, a switch is flooded with packets, each containing different source MAC addresses. The intention is to consume the limited memory set aside in the switch to store the MAC address-to-physical port translation table.

The result of this attack causes the switch to enter a state called failopen mode, in which all incoming packets are broadcast out on all ports (as with a hub), instead of just down the correct port as per normal operation. A malicious user could then use a packet sniffer (such as Ethereal) running in promiscuous mode to capture sensitive data from other computers (such as unencrypted passwords, e-mail and IM conversations), which would normally not be accessible were the switch operating normally.

[edit] See also

• ARP spoofing, a technique which can also facilitate packet sniffing on switches.