Date: Wed, 18 Jul 2007 09:52:28 +0400 From: Eygene Ryabinkin <rea-fbsd@codelabs.ru> To: Chuck Swiger <cswiger@mac.com> Cc: Julian Elischer <julian@ironport.com>, FreeBSD Net <freebsd-net@freebsd.org>, Julian Elischer <julian@elischer.org> Subject: Re: Wierd networking. Message-ID: <20070718055228.GA4053@void.codelabs.ru> In-Reply-To: <3DBBD4E3-ABEA-451A-8E6A-02E9CBAD6A37@mac.com> References: <469D4C9D.7090302@ironport.com> <469D4FB6.9040609@elischer.org> <3DBBD4E3-ABEA-451A-8E6A-02E9CBAD6A37@mac.com>
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Chuck, Julian, good day.
Tue, Jul 17, 2007 at 04:47:30PM -0700, Chuck Swiger wrote:
> % tcpdump -nS -r IE7.pcap
> reading from file IE7.pcap, link-type EN10MB (Ethernet)
> 18:24:41.313890 IP 172.28.15.82.3128 > 10.251.22.29.1121: . ack 1573162290 win
> 32120
> 18:24:41.313995 IP 10.251.22.29.1121 > 172.28.15.82.3128: P
> 1573162290:1573162378(88) ack 3799409121 win 65535
> 18:24:41.314015 IP 172.28.15.82.3128 > 10.251.22.29.1121: . ack 1573162378 win
> 33492
> 18:24:41.314072 IP 172.28.15.82.3128 > 10.251.22.29.1121: .
> 3799409121:3799410581(1460) ack 1573162378 win 33580
> 18:24:41.314080 IP 172.28.15.82.3128 > 10.251.22.29.1121: P
> 3799410581:3799410861(280) ack 1573162378 win 33580
> 18:24:41.314118 IP 172.28.15.82.3128 > 10.251.22.29.1121: F
> 3799410861:3799410861(0) ack 1573162378 win 33580
>
> ...at this point, the client should have received the above packets and ACK for
> 3799410862 to include the FIN.
>
> 18:24:41.314744 IP 10.251.22.29.1121 > 172.28.15.82.3128: P
> 1573162378:1573162380(2) ack 3799409121 win 65535
>
> ...instead it sends an ACK for earlier traffic. The Squid box should be in
> FIN-WAIT-1 and simply ignore this as a dup ACK, rather than sending an RST:
Seems like it is the effect of the SS_NOFDREF check in the
netinet/tcp_input.c, at least it is present in the rev. 1.281.2.5.
See the post
http://lists.freebsd.org/pipermail/freebsd-current/2007-July/074837.html
I believe it discuisses the same problem, but for -CURRENT. In
short, Squid child closes the descriptor, so connection is present
in the TCP/IP stack only. And SS_NOFDREF check provokes RST and
invokes tcp_close().
--
Eygene
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