NIC PROMISC mode

It was a little bit strange situation, I found my outer interface in a PROMISC mode.
“ip a” or “ifconfig” output shows that my eth0 interface was in the PROMISC mode, but I don’t understand, why?

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eth0: <broadcast,multicast,promisc,up,lower_up> mtu 1500 ...
</broadcast,multicast,promisc,up,lower_up>

I don’t used tcpdump or similar tools in this moment.
After I spend some time to my favorite search engine, I found how to disable manually this mode:

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ifconfig eth0 -promisc