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    SubjectRe: Weird tcp performance differences with 2.0 and 2.2 kernels
    On Fri, Feb 12, 1999 at 06:15:27AM +0100, David C Niemi wrote:
    > Users are reporting odd and unpleasant FTP hangs on as well,
    > which is now running 2.2.1 with the latest fixed wu-ftpd. These problems
    > did not occur with the 2.0.36 kernel but did with 2.2pre6; I'm not quite
    > sure whether they occured in the 2.1.126-8 era because the UP flu made
    > things unusable back then.
    > The hangs do not ALWAYS happen, they are more likely on more remote
    > connections and on connections via firewalls (in the latter case the
    > connections work fine for a similar FTP server running 2.0.36 and used to
    > work fine for prior to 2.2.x.

    Most likely those firewalls can't handle extended TCP options or they
    are connected via a router with broken VJ header compression. Try
    turning them off with:

    for i in tcp_timestamps tcp_sack tcp_window_scaling ; do
    echo 0 >/proc/sys/net/ipv4/$i

    Those host will have problem with most new TCP stacks though.

    Another possible explanation would be if they block all of ICMP, there
    is a MTU <your interface MTU somewhere on the path and you
    compiled your 2.0.36 without path mtu discovery. In this case you could
    turn it off via /proc/sys/net/ipv4/ip_no_pmtu_disc, but I would recommend
    against it. Not using path mtu discovery adds a significant cost to the


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