. . "For packet-oriented interfaces, the number of packets\nreceived via the interface that were discarded because\nof an unknown or unsupported protocol. For\ncharacter-oriented or fixed-length interfaces that\nsupport protocol multiplexing, the number of\ntransmission units received via the interface that were\ndiscarded because of an unknown or unsupported protocol.\nFor any interface that does not support protocol\nmultiplexing, this counter is not present.\n\nDiscontinuities in the value of this counter can occur\nat re-initialization of the management system, and at\nother times as indicated by the value of\n'last-clear'." . . "Reference : RFC 2863: The Interfaces Group MIB - ifInUnknownProtos" .