Network card working mode

Network

card working mode There are four working modes of the network card, namely:

broadcast (Broadcast) mode
, the frame whose physical address (MAC) address is 0Xffffff is broadcast frame, and the network card working in broadcast mode receives broadcast frame.


Multicast (Multicast) mode
The frame with the multicast delivery address as the destination physical address can be received by other hosts in the group at the same time, but the hosts outside the group cannot receive it. However, if a network card is set to multicast delivery mode, it can receive all multicast delivery frames regardless of whether it is a member of the group or not.


Unicast mode (Unicast)
The network card working in direct mode only receives frames whose destination address is its own Mac address.


Promiscuous mode (Promiscuous)
1. A network card in promiscuous mode can receive all data that passes through it, regardless of whether the data destination address is it.
2. If the working mode of the network card is set to "promiscuous mode" through the program, then the network card will accept all the data frames flowing through it, which is actually the basic principle of Sniffer's work: let the network card receive all the data he can receive.
3. Sniffer is a kind of software that can set the state of the local network card to a promiscuous state. When the network card is in this "promiscuous" mode, the network card has a "broadcast address", and it has a "broadcast address" for every data frame it encounters. A hardware interrupt is generated to alert the operating system to process every packet that flows over the physical medium. It can be seen that Sniffer works at the bottom layer of the network environment, it intercepts all the data being transmitted on the network, and through corresponding software processing, it can analyze the content of these data in real time, and then analyze the network status and overall layout.

ifconfig eth0 promisc set promiscuous
ifconfig eth0 -promisc unpromisc