Date: Fri, 04 Feb 2000 09:08:36 +0000 From: Brian Somers <brian@Awfulhak.org> To: Gene Kan <genehkan@scam.xcf.berkeley.edu> Cc: freebsd-net@FreeBSD.ORG, brian@hak.lan.Awfulhak.org Subject: Re: Non-blocking sockets and network outages Message-ID: <200002040908.JAA00756@hak.lan.Awfulhak.org> In-Reply-To: Message from Gene Kan <genehkan@scam.xcf.berkeley.edu> of "Thu, 03 Feb 2000 22:17:31 PST." <20000204061731.85976.qmail@scam.xcf.berkeley.edu>
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> I've got an interesting problem involving non-blocking sockets and network
> outages. In all cases, SO_KEEPALIVE is on, and
> net.inet.tcp.always_keepalive: 1. The problem manifests itself when
> there is a net partition, the other endpoint loses power, or something of
> that sort. Basically, when a connection dies without first notifying with
> RST or FIN.
>
> If I mark a socket for reading, the fd will just never become active, and
> I have an ESTABLISHED connection (verified with netstat) forever.
>
> If I do a non-blocking write, the write will return -1 with errno==EAGAIN.
> Obviously, since it just looks like the other side isn't slurping up the
> data because I'm not getting a window update.
>
> Finally...I can't figure out why the keepalives aren't taking care of all
> this for me, and discovering the connections are dead. I waited for hours,
> which surely should have been more than all timeouts...
Keepalives are by default very infrequent:
$ sysctl -a | fgrep keepi
net.inet.tcp.keepidle: 7200000
net.inet.tcp.keepintvl: 75000
net.inet.tcp.keepinit: 75000
hak:/sys/netinet $ fgrep KEEPCNT /sys/netinet/*.h
/sys/netinet/tcp_timer.h:#define TCPTV_KEEPCNT 8 /* max probes before drop */
This means that the first keepalive won't be sent for 2 hours, at
which point up to 8 will be sent with 75 seconds in between each. If
there are no responses after that, the connection is dropped.
> Thanks for any help.
>
> Gene
--
Brian <brian@Awfulhak.org> <brian@FreeBSD.org>
<http://www.Awfulhak.org>; <brian@OpenBSD.org>
Don't _EVER_ lose your sense of humour ! <brian@FreeBSD.org.uk>
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