Path: utzoo!attcan!utgpu!watmath!iuvax!rutgers!bellcore!jupiter!karn
From: karn@jupiter (Phil R. Karn)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: TCP/IP close connection TIME_WAIT ?
Message-ID: <17529@bellcore.bellcore.com>
Date: 30 Aug 89 21:35:07 GMT
References: <8908291630.AA21776@tove.umd.edu>
Reply-To: karn@jupiter.bellcore.com (Phil R. Karn)
Organization: Bell Communications Research, Inc
Lines: 15

>[Sandy Murphy's discussion of TCP connection closing]
>	Actually, the TIME_WAIT state is not long enough to ENSURE this.  If 
>A's ACK of B's FIN gets lost, B will retransmit its FIN (at least).  If this gets lost
>as well, it is possible for the 2MSL timer to expire before B retransmits again and
>the FIN arrives at A.  Chances are B will receive a RST in that case, because A
>is CLOSED when the FIN arrives.

You're quite right. In fact, whenever your network has a nonzero packet
loss probability, you can NEVER be absolutely sure that the connection
will close gracefully on both ends. This is not only true with TCP, it's
the case for ANY protocol. Check out the "two-army problem" on page 397
of Tanenbaum's "Computer Networks" text (second edition) for an
explanation.

Phil