[lwip-devel] [bug #36210] lwIP does not elicit an empty ACK when received unacceptable ACK

[Woody Wu]

URL:
  <http://savannah.nongnu.org/bugs/?36210>

                 Summary: lwIP does not elicit an empty ACK when received
unacceptable ACK
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: narke
            Submitted on: Mon 16 Apr 2012 03:45:07 PM GMT
                Category: TCP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: 1.4.0

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Details:

When I was testing the code (1.4.0), I found when lwIP received an
unacceptable acknowledge (ackno == snd_nxt + 1), it output nothing.
But, according to RFC 793, page 36:

   3.  If the connection is in a synchronized state (ESTABLISHED,
   FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT),
   any unacceptable segment (out of window sequence number or
   unacceptible acknowledgment number) must elicit only an empty
   acknowledgment segment containing the current send-sequence number
   and an acknowledgment indicating the next sequence number expected
   to be received, and the connection remains in the same state.

an empty acknowledgment segment should be sent.


I did not test out-of-window segment, but I guess the result should be the
same.




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