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SubjectRe: [PATCH] real fix found? (Re: timestamps, tcp_paws_discard and out of order packets/acks (fwd))
   Date:   Thu, 22 Jul 1999 00:49:47 -0400 (EDT)
From: "Benjamin C.R. LaHaise" <blah@kvack.org>

Ahh, you're right! I went back over RFC1323 and found out that the
code in tcp_replace_ts_recent seems to be the root of this problem.
The comment simply don't jive with the code or my reading of the
rfc.

I have to think about this change some more. There are 3 independant
issues working here.

1) RFC1323 describes the check wrong, as stated by the comment.

2) The rules stated by all RFCs and working drafts do not allow
for best utilization of ACK feedback when ACKs are massively
reordered. This is what my PAWS workaround is trying to
accomplish.

I brought this issue up, with detailed traces, to the tcp-impl
list, showing how detrimental it was to performance.

And the best response I got was "oh that bug, it hurts my head each
time I think about it" So Linux will perform well in these cases
and nobody else will because aparently even the RFC authors
themselves do not care. Note that what Linux does makes the PAWS
check rules for pure-ACKs orthogonal to the out of order data
packet cases.

3) Audrey found some other RTT estimation problems which are being
dealt with too, and these fixes have security implications as well.
(before you could quite easily make a connection believe that the
RTT was some nearly infinite value, effectively making the
connection useless)

Until I can verify that the bug in question is fixed, and the above #3
issues are still addressed, I cannot apply this patch.

Later,
David S. Miller
davem@redhat.com

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