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    SubjectRe: e1000, sshd, and the infamous "Corrupted MAC on input"
    On Thu, Feb 03, 2005 at 11:16:37PM -0500, Ethan Weinstein wrote:
    > Matt Mackall wrote:
    > >On Wed, Feb 02, 2005 at 10:44:14PM -0500, Ethan Weinstein wrote:
    > ...
    > >>Finally, I used a crossover cable between the two boxes, which resulted
    > >>in the same error from sshd again.
    > >
    > >
    > >Well ssh isn't an especially good test as it's hard to debug.
    > >
    > >Try transferring large compressed files via netcat and comparing the
    > >results. eg:
    > >
    > >host1# nc -l -p 2000 > foo.bz2
    > >
    > >host2# nc host1 2000 < foo.bz2
    > >
    > >If the md5sums differ, follow up with a cmp -bl to see what changed.
    > >
    > >Then we can look at the failure patterns and determine if there's some
    > >data or alignment dependence.
    > >
    > Excellent tip, thanks. I was able to reprodce the problem several times
    > using this technique with nc, however the problem was intermittent (as
    > nasty problems like this often are). I used a 1.3G gzipped tarball and
    > experienced several botched transfers along with a few good ones. To
    > be fair, I also switched back to 100Fdx and repeated; I didn't get a
    > single failure at this speed over 25 or so runs.
    > The results of two cmp's are here:
    > What next?

    Ok, reproduceable without ssh makes narrowing this down much easier.
    Are you seeing errors on the interface? No would indicate problems
    post CRC checking on the receive side. Do errors happen in both
    directions? If not, it may be CPU speed-related or specific to a given
    NIC - swap them if they're not onboard.

    The next test is to send patterns. Try sending yourself a gigabyte of:

    #include <stdio.h>

    int main(void)
    int i;

    for (i = 0; i < 0x10000000; i++) {
    fwrite(&i, 4, 1, stdout);

    If there's some sort of partial DMA transfer going on, this should
    make it evident.

    Mathematics is the supreme nostalgia of our time.
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