Why might a network interface (NIC) be in "promiscuous mode" and what does it mean?

Solution Verified - Updated -

Issue

  • Need to know the meaning of the following messages:

    Feb 24 12:15:14 server kernel: device eth0 entered promiscuous mode
    Feb 24 12:15:39 server kernel: device eth0 left promiscuous mode
    
  • My NIC card has the PROMISC flag set in ip and ifconfig output:

    # ip link show eth0
    2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
        link/ether 52:54:00:4b:72:87 brd ff:ff:ff:ff:ff:ff
    
  • Hundreds of messages device ethX left promiscuous mode

  • How to avoid the promiscuous mode messages being logged repeatedly?

Environment

  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 4

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