Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!OKEEFFE.BERKELEY.EDU!karels
From: karels@OKEEFFE.BERKELEY.EDU (Mike Karels)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SO_KEEPALIVE considered harmful?
Message-ID: <8906082328.AA04514@okeeffe.Berkeley.EDU>
Date: 8 Jun 89 23:28:37 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 39

Sorry, I can't let this go by without commenting on Phil's message
and this discussion, even though the discussion has mostly died down.
(I haven't been reading tcp-ip very often, but noticed this subject
line going by.)

Last time Phil and I talked about keepalives in person, I asked him
whether he had problems with telnet/rlogin servers accumulating on
his systems if they didn't use keepalives.  We certainly accumulate
junk, including xterm programs, waiting for input from a half-open
connection.  Phil told me that he doesn't have problems, because
he runs a "wall" every night to force output to all users, and of
course breaking connections that time out.  In other words, Phil
violently objects to servers requesting keepalives from TCP, but
allows the system manager (himself) to force them above the application
level.  And before people jump up to point out the difference in time
scales, the current BSD code sends no keepalive packets until a connection
has been idle for 2 hr, and that interval is easily changeable.
One proposal for the Host Requirements document was to wait for 12 hr.
I think that's a bit high, but the difference is only a factor of 6.
Compare the number of keepalive packets with the number of packets
exchanged by an xterm and an X server over the course of a week
if used 4 hours a day!

Phil says:
	... I'd go a little further, though,
	and say that a REMOTE USER (not just the application code) must always
	be able to turn off keepalives, even on binary-only systems. It does no
	good to say "the application must be able to disable keepalives" when
	I'm having problems with a remote server that I have no administrative
	control over.

I'm sorry, Phil, but remote users have no more right to override system
management policies than do local users (at least on *our* systems!).
On some of the systems where I have guest accounts, local or remote
users are logged off if they aren't active for two hours.  I don't like
that, either, but I don't claim that the managers of those systems
have no right to enforce such a policy.

		Mike