Eygene Ryabinkin wrote:
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().
I think your analysis is correct. Have to find out who to deal properly
with a closed socket before the TCP is closed as well.
--
Andre
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