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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 ftp.tux.org 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 ftp.tux.org 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
done

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
network.

-Andi

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