TCP LAST-ACK state broken in 2.4.17-pre2

From: Mika Liljeberg (
Date: Mon Dec 10 2001 - 13:16:07 EST


I came across the following behavior (sorry, no tcpdump but this should
be easy to reproduce with the right tools):

hostA hostB
  --------ACK-------X (packet lost)
  <-----data+FIN--------- (retransmit)
  <-----data+FIN--------- (retransmit)
  <-----data+FIN--------- (retransmit)
  <-----data+FIN--------- (retransmit)

HostA is running Linux 2.4.17-pre2. HostB is running Symbian OS. All the
sequence numbers pan out.

Either LAST-ACK is completely broken or Linux just cannot handle a
FIN-ACK that is piggybacked on a data segment, when received in LAST-ACK
state. It should be acked as an out-of-window segment, as usual.
Finally, the LAST-ACK state times out and Linux responds to the FIN
segment with an RST.


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This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:18 EST