Re: 2.1.129: "TCPv4 bad checksum" errors with PPP

Jim Gettys (jg@pa.dec.com)
Mon, 23 Nov 1998 12:50:46 -0800


> Sender: owner-linux-kernel@vger.rutgers.edu
> From: Brendan Cully <brendan@kublai.com>
> Date: Mon, 23 Nov 1998 11:58:15 -0500
> To: linux-kernel@vger.rutgers.edu
> Subject: Re: 2.1.129: "TCPv4 bad checksum" errors with PPP
> -----
> On Monday, 23 November 1998 at 12:19, Jamie Lokier wrote:
> > I wrote:
> > > Since 2.1.127 or thereabouts, I've noticed lots of "TCPv4 bad checksum"
> > > errors in my kernel logs. This is over a PPP connection.
> > >
> > > I know that there are supposed to be bugs with some ISPs VJ header
> > > compression, so I disabled it at the Linux end with "novj".
> > > Unfortunately, there are still checksums errors with VJ header
> > > compression disabled. :-(
> >
> > I thought I'd add that I *am* using hdparm -u1, that's not the problem
> > either.
> >
> Me too! :)

I saw on end-to-end interest list a while back that there is a (currently
unexplained) lot of packets with bad checksums floating around the net
at the moment. They are trying to diagnose the problem at the moment.

One out of 7000 is pretty bad. You might see if the frequency you see
is similar to that Craig Partridge reports.

The message is attached.
- Jim

> Sender: owner-end2end-interest@ISI.EDU
> From: Craig Partridge <craig@aland.bbn.com>
> Date: Fri, 02 Oct 1998 12:29:50 -0700
> To: end2end-interest@ISI.EDU
> Subject: looking for a student to join checksum study
> -----
> Hi folks:
>
> Jonathan Stone and I have been slowly working for a good bit of this year
> on the checksum failure problem that Vern Paxson identified. In brief,
> the problem is that about 1 in 7,000 datagrams has a bad transport checksum
> value and we are trying to understand why the failure rate is that high.
>
> Unfortunately, due to lack of time, Jonathan and I have not been making
> progress at the rate we would like to. The purpose of this note is to
> see if there's someone in the E2E community (presumably, but not necessarily,
> a student) who'd like to help us out and get the basic work done.
>
> We believe we have new packet capture software written that runs (though
> the new person would have to check it to confirm we're right) and we're close
> to being able to run it on some systems which have large amounts of traffic
> running past them. We have also been offered access to a variety of
> traffic dumps. That will give us a bunch of dumps to pore through (perhaps
> with new software required) to detect the types of errors occuring.
> So expertise with C and some understanding of IP/TCP/UDP packet formats
> is required.
>
> Assuming we actually learn something interesting the new person would
> co-author a journal paper with us about the results. (Warning: there's
> no promise the results will be interesting -- there's still a substantial
> chance that the result will be "there's a bug in release 3.14159 of
> So-and-So's kernel").
>
> If this sounds of interest, drop me a note.
>
> Thanks!
>
> Craig
>
> E-mail: craig@aland.bbn.com or craig@bbn.com

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