As promiscuous mode can be used in a malicious way to sniff on a network, one might be interested in detecting network devices that are in promiscuous mode. In promiscuous mode, some software might send responses to frames even though they were addressed to another machine. However, experienced sniffers can prevent this (e.g., using carefully designed firewall settings). An example is sending a ping (ICMP echo request) with the wrong MAC address but the right IP address. If your firewall blocks all ICMP traffic, this will be prevented.

promiscous mode is one in which all the packets are sent to a computer and not only those which are addressed to it.

in a non promiscous mode only those packets are send to the computer which are addressed to it.

Please help

Inline is used to look at a specific location such as between two routers, where as promiscuous mode captures traffic using a capture device such as a hub or switch, this way all traffic that goes through the device is monitored.

Promiscuous mode