Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!bloom-beacon!EXPO.LCS.MIT.EDU!rws
From: rws@EXPO.LCS.MIT.EDU
Newsgroups: comp.windows.x
Subject: Re: Why does X not use SO_KEEPALIVE?
Message-ID: <8905241247.AA00833@expire.lcs.mit.edu>
Date: 24 May 89 12:47:32 GMT
References: <7992@boring.cwi.nl>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 27


    Is there a good reason not to set SO_KEEPALIVE?

I've probed a TCP/IP wizards list about this.  While there doesn't seem to be
unanimity, there is clearly a sizable contingent that believe this feature is
evil, and that even it is deemed necessary in certain situations,
"indiscriminant" use (e.g. automatically in all X connections) is evil.
Here are excerpts from a draft Requirements for Internet Hosts RFC:

	Implementors MAY include "keep-alives" in their TCP
	implementations, although this practice is not universally
	accepted.  If keep-alives are included, the application MUST
	be able to turn them on or off for each TCP connection, and
	they MUST default to off.

	The TCP specification does not include a keep-alive
	mechanism because it could:  (1) cause perfectly good
	connections to break during transient Internet
	failures; (2) consume unnecessary bandwidth ("if no one
	is using the connection, who cares if it is still
	good?"); and (3) cost money for an Internet path that
	charges for packets.

	A TCP keep-alive mechanism should only be invoked in
	network servers that might otherwise hang indefinitely
	and consume resources unnecessarily if a client crashes
	or aborts a connection during a network partition.