Re: Massive TCPv4 bad checksum

Andi Kleen (ak@muc.de)
18 Oct 1998 12:45:41 +0200

In article <m0zUl2h-000396C@ocean.lucon.org>,
hjl@lucon.org (H.J. Lu) writes:
>>
>> On Sat, 17 Oct 1998, H.J. Lu wrote:
>>
>> > I have massive TCPv4 bad checksum on my CSLIP link from
>> > my CSLIP server to my machine ever since I upgraded to
>> > linux 2.1.1xx. Any suggestions?
>>
>> 2.0 just never spat out a message when it got a bad checksum, so this is
>> probably why you never saw it before. If you're noticing that there's an
>> actual packet data problem that didn't exist before with 2.0, then you
>> might want to investigate. The message will be probably be removed by
>> 2.2.
>>

> I can tell my SLIP speed is slower than 2.0 and there are quite
> some corrupted packets come over SLIP link.

Some broken modem server have buggy VJ compression functions that can't
cope with the new RFC1323/SACK TCP options Linux 2.1 sends. Try turning
them off with

echo 0 >/proc/sys/net/ipv4/tcp_sack
echo 0 >/proc/sys/net/ipv4/tcp_timestamps
echo 0 >/proc/sys/net/ipv4/tcp_window_scaling

Will only take effect for new TCP connections afterward.

BTW, you can check for checksum errors even on 2.0 with a newer nettools
and netstat -s or by directly looking at /proc/net/snmp.

-Andi

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/