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Promiscuous Interface and Broadcasting

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• Miscellaneous topics
  • In the final webpage on Ethernet, I will discuss 2 random topics:

    Promiscuous/Non-promiscuous ports Broadcasting

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• The non-promiscuous Ethernet Interface:
  • Recall:

    An Ethernet network interface card (NIC) has a unique Ethernet Address The Ethernet card can recognize its own network address and accept only the Ethernet frames that contains its network address

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  • Nomenclature:

    Non-promiscuous interface = a network interface that accepts only frames with its network address as destination

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  • There is another type of Ethernet Interface:

    The promiscuous interface (which is found on bridges and Ethernet switches)

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• Operation of a Non-promiscuous Ethernet Interface:
  • A Non-promiscuous port or interface will read the destination address in an Ethernet frame.

  • If the destination address matches the Ethernet Address of the interface, then the interface will accept (and process) the Ethernet frame.

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• Operation of a Promiscuous Ethernet Interface:
  • Promiscuous port:

    Promiscuous port = a network interface that accepts every frame (and process it)

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  • Difference between promiscuous and non-promiscuous port illustrated:

    A non-promiscuous port E6 will not accept a frame destined for E4: A promiscuous port E6 will accept (and process) a frame destined for another destination E4:

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• Difference between Ethernet bridges/switches and Ethernet hosts
  • Facts:

    Ethernet bridges/switches have promiscuous ports (because a bridge must process all messages --- even those that does not contain the MAC address of the bridge) Ethernet hosts (e.g., computer) have non-promiscuous ports

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• Broadcasting
  • Broadcasting:

    Broadcasting = transmit a frame to all nodes in the network (I.e., all nodes will accept the frame and process it)

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  • Ethernet (and token ring) networks has a built-in broadcast capability

    That's because a frame will reach all nodes in the network !!! Some network features (discussed later) will exploit this inherent broadcast capability

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  • Addressing all node in the network:

    Broadcast address = a special network address used to identify every node in the network

    Broadcast address of Ethernet:

    Ethernet broadcast address = 11111111 11111111 11111111 11111111 11111111 11111111

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  • Example: broadcasting