Answer Description
When a NIC is placed in promiscuous mode, it will pass all data it receives onto the CPU. Normally, a NIC will ignore data not intended for it's IP or MAC Addresses.
Wikipedia
In computer networking, promiscuous mode is a mode for a wired network interface controller (NIC) or wireless network interface controller (WNIC) that causes the controller to pass all traffic it receives to the central processing unit (CPU) rather than passing only the frames that the controller is specifically programmed to receive This mode is normally used for packet sniffing that takes place on a router or on a computer connected to a wired network or one being part of a wireless LAN Interfaces are placed into promiscuous mode by software bridges often used with hardware virtualization In IEEE 802 networks such as Ethernet or IEEE 802
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