Fast retransmit problem

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To: <freebsd-net@freebsd.org>
Date: Wed, 30 Jul 2003 11:09:09 -0700

I am facing a peculiar problem. Here is the scenario.
                   During a tcp data transfer.An intermediate data
packet(Say X) from server to client is lost.The client sends an ack with
ACK no. corresponding to the lost segment.Now this continues till the
no. of duplicate acks reach the threshold.But Just before the threshold
is reached, the server sent a fin to Client.After the FIN is sent the
server realized that the packet X is lost and it retransmits the
packet.Now if we assume that the Sequence no. of FIN packet is 100.The
client should actually send the Final ACK with ACK no. as 101.But
because of a bug , the client sends the Last ACK with ACK no. 100.In
ideal cases since the FIN is not acked..the server should be
retransmitting the FIN.But it does not.Upon investigating the Scene, i
found that the retransmit timer is not running anymore.This is easily
reproducible in my environment.I know that the timer is stopped just
before the Fast retransmit happens, i think that the timer should be
restarted once the ack is received but i am not able to figure out where
it should be restarted..Did anybody face this problem already? Is this a
known bug ?. Server is a FreeBSD 4.6 machine and the client is Windows
2000
 
Thanks in advance
 
Sreekanth
 
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