Understand the promiscuous mode in the operating mode of the NIC

Promiscuous mode, the English name is promiscuous mode, which refers to a machine that can receive all of its data streams, regardless of whether the destination address contained in the data stream is itself, this pattern corresponds to a non-promiscuous mode. In non-promiscuous mode, the network adapter listens only for traffic on its own MAC address. In promiscuous mode, it can listen on all packets. By default, the network adapter is set to non-promiscuous mode. Promiscuous mode is a security policy in the Data Link layer (L2).

The NIC in promiscuous mode can receive all traffic through it, no matter what format, address (any packet transmitted in the same conflict domain), after receiving the packet by the network layer determines how the packet is handled, such as whether it is submitted to the upper processing or to the lower level forwarding or discard. Instead of promiscuous mode, the network card only sends its own packets (including broadcast packets) to the upper layer, and all other packets are discarded.

To give a simple example, a switch is connected to 3 computers, respectively, C1, C2 and C3, non-promiscuous mode C1 to C2 send packets C3 is not received, and in promiscuous mode C1 to C2 send packets C3 can receive, at this time C3 is a network listener (stealing listeners), And this kind of monitoring C1 and C2 is not aware of. Therefore, the person in the promiscuous mode is called the listening mode.

According to network data, the NIC has four modes, namely broadcast mode, multicast mode, promiscuous mode and non-promiscuous mode (direct mode). Specifically, you can refer to Google.

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Understand the promiscuous mode in the operating mode of the NIC