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Date: Fri, 1 Nov 1996 17:06:00 +0800 (WST)
From: Peter Wemm <peter@spinner.DIALix.COM>
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Subject: kern/1940: TCP doesn't time out of FIN_WAIT_1 and floods packets.
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>Number:         1940
>Category:       kern
>Synopsis:       TCP doesn't time out of FIN_WAIT_1 and floods packets.
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Nov  1 01:10:01 PST 1996
>Last-Modified:
>Originator:     Peter Wemm
>Organization:
not.
>Release:        FreeBSD 2.2-CURRENT i386
>Environment:

Machine built from -current sources within the last week.  The machine is
running a web proxy server (squid-1.1.beta).

>Description:

An unusual jump in network outbound network traffic turned out to be caused
by a -current machine with a stuck connection.

The proxy server had initiated the connection:
Active Internet connections
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
[..]
tcp        0    366  fermi.29485            kaos.http  FIN_WAIT_1
[..]

I am not sure of the sequence of events that lead to this getting in this
state, but it was running this sequence of packets, even after squid had
closed the connection (and even after having been killed):

peter@fermi[8:27am]/home/squid-125# tcpdump -s 1500 -N 
tcpdump: listening on ed0
08:28:26.419290 kaos.http > fermi.29485: . ack 2272139 504 win 9112 (DF)
08:28:26.419459 fermi.29485 > kaos.http: F 0:0(0) ack 4294967090 win 17280 <nop,nop,timestamp 371690 324020,nop,nop,cc 21426> (DF)
08:28:26.426922 kaos.http > fermi.29485: . ack 1 win 9112 (DF)
08:28:26.427038 fermi.29485 > kaos.http: F 0:0(0) ack 4294967090 win 17280 <nop,nop,timestamp 371690 324020,nop,nop,cc 21426> (DF)
08:28:26.435747 kaos.http > fermi.29485: . ack 1 win 9112 (DF)
08:28:26.435877 fermi.29485 > kaos.http: F 0:0(0) ack 4294967090 win 17280 <nop,nop,timestamp 371690 324020,nop,nop,cc 21426> (DF)
08:28:26.445638 kaos.http > fermi.29485: . ack 1 win 9112 (DF)
08:28:26.445750 fermi.29485 > kaos.http: F 0:0(0) ack 4294967090 win 17280 <nop,nop,timestamp 371690 324020,nop,nop,cc 21426> (DF)
08:28:26.454399 kaos.http > fermi.29485: . ack 1 win 9112 (DF)
08:28:26.454548 fermi.29485 > kaos.http: F 0:0(0) ack 4294967090 win 17280 <nop,nop,timestamp 371690 324020,nop,nop,cc 21426> (DF)
[...]

I presume this is a half-close, what is meant to happen here?

>How-To-Repeat:

Unknown, but I hope it doesn't.. :-]

>Fix:
	
It seems that the tcp connection managed to get into a state where both
ends were out of sync.  I don't know my tcp states well enough to
understand what is meant to happen here, but hanging in FIN_WAIT_1 forever
doesn't seem nice.

>Audit-Trail:
>Unformatted: