Re: Odd TCP problems with 2.2.x

From: Austin Schutz (
Date: Fri Mar 17 2000 - 02:38:51 EST

> The second is after ursula notices that it got no ack for the first.
> They have the same data, but the first try at sending the segment did
> not have the tcp timestamp options. Instead ursula (or somebody)
> filled that area with a bunch of zeroes (option <eol>).
        It might be interesting to see if I can find a machine to try
and see if I can see what it thinks it is sending out.
        The one machine I can think of that I have root access on that
is not behind a bizarro firewall and not on my local net doesn't seem to
exhibit the problem. It is a solaris 2.6 (with suggested patches) machine.

> Ursula and peace did both negotiate sack and timestamp at the beginning
> of the transfer, but then ursula doesn't send timestamp sometimes. When
> it does, it gets them correct. Should it not be the case that a tcp
> receiver should just accept the packet even if there's no timestamp?
        Gregory Maxwell <> had the most helpful suggestion of
turning off timestamps by doing:

echo -n 0 > /proc/sys/net/ipv4/tcp_timestamps

        which worked like a charm, as you might imagine. Much faster than
my old sparc ever was :-)
> Are you doing anything funky with filtering in your LAN? Can you also
> take a look at /proc/net/snmp and see if the Tcp InErrs counter goes up
> during such a session? I wonder if the checksum is off. My test ftp
> to ursula did not exhibit the oddness you're seeing.

        No, nothing funky at all. Yes, the errors counter does increase.


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