Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!proteon.com!jas
From: jas@proteon.com (John A. Shriver)
Newsgroups: comp.protocols.tcp-ip
Subject: SO_KEEPALIVE considered harmful?
Message-ID: <8906011416.AA14730@monk.proteon.com>
Date: 1 Jun 89 14:16:47 GMT
References: <19890525225353.2.BARMAR@OCCAM.THINK.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 18

The user (client) Telnet in the MIT UNIX V6 TCP/IP (one of those
pre-Bezerkely WAN TCP/IP's) would periodically print:

	Host not responding, type ^^q to quit

on the user's terminal when (and only when) it had outstanding data to
send, and could not get it acknowledged.  If you had reason to beleive
it was right, you aborted the connection.  Otherwise, it sat there
retransmitting at a slow rate until connectivity was regained.
Meanwhile, you would go and fix the broken router, and *would not lose
your current session* on the remote host.

Now, if the server Telnet gets into a pickle, it would probably just
abort and die.  That UNIX lacks any way to preserve a login session is
it's problem, MIT AI ITS (on PDP-10's) knew exactly how to preserve
your state when this happened.  Of course, most systems are not in the
habit of generating unsolicited output, so this didn't happen as
often.