IP Checksum Offload

Discussion in 'Linux Networking' started by Bob, Jul 6, 2005.

  1. Bob

    Bob Guest


    I am trying to understand IP checksum offload. I got into this while trying
    to track down a networking problem. I noticed many "IP checksum
    errors" (using iptraf). I think that sent me down the wrong path because I
    am starting to believe this is normal since iptraf looks at the packets
    before the checksum is actually generated. (I got that idea from an
    ethereal FAQ.)

    But this leaves me with a question -- why do I not *always* get IP checksum
    errors? I can run a network test for hours without one checksum error, but
    if I crank up the network activity I start to see them.

    Could it be that checksum offload is only invoked when the network load gets
    to a certain rate? This might make sense since I have read that although
    checksum offload gives a performance boost it does so at the expense of
    less effective checking (since the checksum is generated later in the
    process). Might the driver turn it on and off as load changes?

    I have a Dell Precision 360 with a gigabit ethernet on the motherboard
    (Intel using the e1000 driver).

    SuSE 9.3 with SMP kernel (for hyperthread support).

    Here is output from "ethtool -k eth0"

    # ethtool -k eth0
    Offload parameters for eth0:
    rx-checksumming: on
    tx-checksumming: on
    scatter-gather: on
    tcp segmentation offload: on

    Thanks for any info or leads!

    Bob, Jul 6, 2005
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