Date: Tue, 1 Jun 1999 15:02:47 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Poul-Henning Kamp <phk@FreeBSD.ORG> Cc: current@FreeBSD.ORG Subject: Re: net.inet.tcp.always_keepalive on as default ? Message-ID: <199906012202.PAA84865@apollo.backplane.com> References: <20883.928262460@critter.freebsd.dk>
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Sheesh, talk about a topic to generate noise!
I think keepalive's could easily be turned on by default. At BEST, one
of the first things I did 5 years ago was to turn them on permanently
on all of our machines.
The reason is simple: Without keepalives you can end up with stale
connections that hang forever due to users hanging up their modems without
disconnecting telnet, pop, and other assorted sessions.
Turning on keepalives will produce NO DISCERNABLE INCREASE IN NETWORK
TRAFFIC. Period. Anybody who says they do doesn't understand how
keepalives work. You could have a thousand active connections and
it still wouldn't show a discernable increase.
Daemons do not usually bother to turn on per-connection keepalives. I
do not consider this a bug in the daemon, but instead simply a "the default
nature of this daemon is to use the default keepalive state assigned to
the system as a whole". Simple. Not a bug. We should NOT go around
trying to 'fix' all of our daemons.
The only argument against turning on keepalives by default is that
occassionally someone will expect their telnet to hang around after the
network inbetween them and the remote site has been down for hours.
This used to be a HUGE argument in the days where networks were less
reliable and dialup lines were scarse. It is not an argument now,
however.
Whatever we do, we should not start messing around with the internals
of the kernel trying to 'fix' a non-problem. Keepalives work just dandy
as they are currently implemented, we do not have to mess with it beyond
possibly changing the default in rc.conf.
-Matt
Matthew Dillon
<dillon@backplane.com>
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