[j-nsp] understanding PFE "Hardware input drops" on M10i(CFEB, Internet Processor II)

[Martin T]

Hi,

"Hardware input drops" counter in "show pfe statistics traffic" output
increases rapidly in case one floods router interface with small UDP
datagrams. "Software input medium drops" counter increases as well.
"show pfe statistics traffic" output can be seen below:

root at M10i> show pfe statistics traffic
Packet Forwarding Engine traffic statistics:
    Input  packets:           1587589319                65240 pps
    Output packets:           1330946214                  771 pps
Packet Forwarding Engine local traffic statistics:
    Local packets input                 :             14439730
    Local packets output                :              5902958
    Software input control plane drops  :                    0
    Software input high drops           :                    0
    Software input medium drops         :              6603218
    Software input low drops            :                    0
    Software output drops               :                 2467
    Hardware input drops                :            205506491
Packet Forwarding Engine local protocol statistics:
    HDLC keepalives            :                    0
    ATM OAM                    :                    0
    Frame Relay LMI            :                    0
    PPP LCP/NCP                :                    0
    OSPF hello                 :                    0
    OSPF3 hello                :                    0
    RSVP hello                 :                    0
    LDP hello                  :                  230
    BFD                        :              3505972
    IS-IS IIH                  :               140941
    LACP                       :               566167
    ARP                        :                40372
    ETHER OAM                  :                    0
    Unknown                    :                    0
Packet Forwarding Engine hardware discard statistics:
    Timeout                    :                    0
    Truncated key              :                    0
    Bits to test               :                    0
    Data error                 :                    0
    Stack underflow            :                    0
    Stack overflow             :                    0
    Normal discard             :             15382993
    Extended discard           :                    0
    Invalid interface          :                    0
    Info cell drops            :                    0
    Fabric drops               :                    0
Packet Forwarding Engine Input IPv4 Header Checksum Error and Output
MTU Error statistics:
    Input Checksum             :                  707
    Output MTU                 :                    0

root at M10i>


As much as I have read various documents(for example
http://www.gossamer-threads.com/lists/nsp/juniper/7292), this seems to
be rather platform dependent.
What does "Hardware input drops" mean on M10i with CFEB(Internet
Processor II, FEB-M10i-M7i-S)?


regards,
martin