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Re: NetBSD and SACK?

Fredrik Pettai <> writes:

> On Jan 29, 2010, at 6:08 PM, Andreas Gustafsson wrote:
>> Matthias Scheler wrote:
>>> Are you using hardware checksum offload on that "re0" interface?
>>> If you do please try to disable it and reenable SACK.
>> My hardware, network topology, and NetBSD version have all changed
>> since 2008, and now when I try to reproduce the problem, I find that I
>> am unable to do so.  Apparently whatever was broken has been fixed
>> either in NetBSD or by the hardware changes.  I have now re-enabled
>> SACK on all my NetBSD systems, and if the problem recurs, I will file
>> a PR.
> Before I forget to ask, which NetBSD version are you using with a
> functioning SACK?
> We had problems with SACK on NetBSD 5.0_RC... something,
> not sure that we ever came to test 5.0_RELEASE or later...

SACK is hairy and I can certainly believe there are bugs.  But I have
looked at tcpdump traces (with tcpdump2xplot) and seen sack blocks and
retransmits that look ok.

I am still a bit suspicious of whether the choice of how much and what
to retransmit under multiple losses is exactly correct.  But I can't
make an argument, even incoherent, that it's wrong.

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