Promiscuous mode, in computer related fields, is generally used to refer to the practice of putting a network card into a setting so that it passes all traffic it receives to the CPU rather than just packets addressed to it. Many operating systems require superuser privileges to operate in promiscuous mode. A non-routing node in promiscuous mode can generally only monitor traffic to and from other nodes within the same collision domain (for Ethernet and Wireless LAN) or ring (for Token Ring or FDDI), which is why network switches are used to combat malicious use of promiscuous mode. A router may monitor all traffic that it routes. Promiscuous mode is commonly used to diagnose network connectivity issues. Some programs like ethereal, tcpdump, and airsnort (for wireless LANs) make use of this feature to show the user all the data being transferred over the network. Some programs like FTP and Telnet transfer data and passwords in clear text, without encryption, and network scanners can see this data. Therefore, computer users are encouraged to stay away from programs like telnet and use more secure ones such as SSH.

See Also: Packet sniffer, Wireless sniffer