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Subject: [Bug 203663] [tcp] Incorrect dupack processing to detect loss
Date: Fri, 09 Oct 2015 19:32:05 +0000
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X-Bugzilla-Version: 11.0-CURRENT
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X-Bugzilla-Severity: Affects Many People
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203663

            Bug ID: 203663
           Summary: [tcp] Incorrect dupack processing to detect loss
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs@FreeBSD.org
          Reporter: hiren@FreeBSD.org

Quoting Randall:
"When we recognize a dup-ack we *will not* recognize it if for example if the
rwnd changes even if new SACK information is reported in the sack blocks. This
is due to the fact that in non-SACK you don't (on purpose) recognize ACK?s
where the window changed (since you can?t really tell if its a plain window
update or a dup-ack).. This means we occasionally miss out on stroking the
dup-ack counter and getting out of recovery...."

Another report of the same/similar problem:
https://lists.freebsd.org/pipermail/freebsd-net/2015-September/043387.html

This bug leads to us detecting loss later than we should have. And that leads
to suboptimal loss recovery as a whole.

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