connection reset after second syn-ack was sent (FreeBSD 7.0)

[Holger Kipp]

Hello,

I have a little problem here that is driving me nuts:

I occasionally experience the following:
2008-04-18 10:38:46.454495 IP 192.168.1.1.55784 > 192.168.188.188.515: S 2765551688:2765551688(0) win 32768 <mss 1460,wscale 0,nop>
2008-04-18 10:38:46.454507 IP 192.168.188.188.515 > 192.168.1.1.55784: S 3468383339:3468383339(0) ack 2765551689 win 65535 <mss 1460,nop,wscale 3>
2008-04-18 10:38:49.453868 IP 192.168.188.188.515 > 192.168.1.1.55784: S 3468383339:3468383339(0) ack 2765551689 win 65535 <mss 1460,nop,wscale 3>
2008-04-18 10:38:49.722767 IP 192.168.1.1.55784 > 192.168.188.188.515: . ack 1 win 32768
2008-04-18 10:38:49.722786 IP 192.168.188.188.515 > 192.168.1.1.55784: R 3468383340:3468383340(0) win 0
2008-04-18 10:38:49.727926 IP 192.168.1.1.55784 > 192.168.188.188.515: P 1:7(6) ack 1 win 32768
2008-04-18 10:38:49.819709 IP 192.168.188.188.515 > 192.168.1.1.55784: P 1:2(1) ack 7 win 65535
2008-04-18 10:38:50.006543 IP 192.168.1.1.55784 > 192.168.188.188.515: R 2765551695:2765551695(0) win 0

and

2008-04-18 15:30:31.256246 IP 192.168.1.1.53597 > 192.168.188.188.515: S 1236263266:1236263266(0) win 32768 <mss 1460,wscale 0,nop>
2008-04-18 15:30:31.256257 IP 192.168.188.188.515 > 192.168.1.1.53597: S 559988198:559988198(0) ack 1236263267 win 65535 <mss 1460,nop,wscale 3>
2008-04-18 15:30:34.255479 IP 192.168.188.188.515 > 192.168.1.1.53597: S 559988198:559988198(0) ack 1236263267 win 65535 <mss 1460,nop,wscale 3>
2008-04-18 15:30:34.440092 IP 192.168.1.1.53597 > 192.168.188.188.515: . ack 1 win 32768
2008-04-18 15:30:34.440112 IP 192.168.188.188.515 > 192.168.1.1.53597: R 559988199:559988199(0) win 0
2008-04-18 15:30:34.496849 IP 192.168.1.1.53597 > 192.168.188.188.515: P 1:7(6) ack 1 win 32768
2008-04-18 15:30:34.596461 IP 192.168.188.188.515 > 192.168.1.1.53597: . ack 7 win 65535
2008-04-18 15:30:34.620914 IP 192.168.188.188.515 > 192.168.1.1.53597: P 1:2(1) ack 7 win 65535
2008-04-18 15:30:34.780723 IP 192.168.1.1.53597 > 192.168.188.188.515: R 1236263273:1236263273(0) win 0
2008-04-18 15:30:34.804966 IP 192.168.1.1.53597 > 192.168.188.188.515: R 1236263273:1236263273(0) win 0

(IP addresses changed to protect the innocent ;-)

Can anyone enlighten me as to why the freebsd printserver (192.168.188.188) is sending
a reset after ack had been received - this only happens if no answer was received for the
first syn-ack reply, so a second one is send out?

System is 7.0-RELEASE out of the box on a single-processor 2.4GHz P4 Compaq with 1 GB
main memory, with lpd configured.


Here the usual behaviour (I would expect this to be the same even with two syn-acks send back):

2008-04-18 10:38:47.921055 IP 192.168.1.1.55786 > 192.168.188.188.515: S 2765866087:2765866087(0) win 32768 <mss 1460,wscale 0,nop>
2008-04-18 10:38:47.921081 IP 192.168.188.188.515 > 192.168.1.1.55786: S 4178311531:4178311531(0) ack 2765866088 win 65535 <mss 1460,nop,wscale 3>
2008-04-18 10:38:48.389707 IP 192.168.1.1.55786 > 192.168.188.188.515: P 1:7(6) ack 1 win 32768
2008-04-18 10:38:48.488906 IP 192.168.188.188.515 > 192.168.1.1.55786: . ack 7 win 8211
2008-04-18 10:38:49.760593 IP 192.168.188.188.515 > 192.168.1.1.55786: P 1:2(1) ack 7 win 8212
2008-04-18 10:38:49.945735 IP 192.168.1.1.55786 > 192.168.188.188.515: P 7:26(19) ack 2 win 32768
2008-04-18 10:38:49.946002 IP 192.168.188.188.515 > 192.168.1.1.55786: P 2:3(1) ack 26 win 8212
2008-04-18 10:38:50.236467 IP 192.168.1.1.55786 > 192.168.188.188.515: P 26:1050(1024) ack 3 win 32768
2008-04-18 10:38:50.244742 IP 192.168.1.1.55786 > 192.168.188.188.515: P 1050:2074(1024) ack 3 win 32768
2008-04-18 10:38:50.244762 IP 192.168.188.188.515 > 192.168.1.1.55786: . ack 2074 win 8084
2008-04-18 10:38:50.253217 IP 192.168.1.1.55786 > 192.168.188.188.515: P 2074:3098(1024) ack 3 win 32768
2008-04-18 10:38:50.261559 IP 192.168.1.1.55786 > 192.168.188.188.515: P 3098:4122(1024) ack 3 win 32768
2008-04-18 10:38:50.261571 IP 192.168.188.188.515 > 192.168.1.1.55786: . ack 4122 win 8084
[..]
2008-04-18 10:38:51.236260 IP 192.168.1.1.55786 > 192.168.188.188.515: P 26200:26201(1) ack 5 win 32768
2008-04-18 10:38:51.236271 IP 192.168.188.188.515 > 192.168.1.1.55786: . ack 26201 win 8212
2008-04-18 10:38:51.236289 IP 192.168.188.188.515 > 192.168.1.1.55786: P 5:6(1) ack 26201 win 8212
2008-04-18 10:38:51.539638 IP 192.168.1.1.55786 > 192.168.188.188.515: F 26201:26201(0) ack 6 win 32768
2008-04-18 10:38:51.539667 IP 192.168.188.188.515 > 192.168.1.1.55786: . ack 26202 win 8212
2008-04-18 10:38:51.539713 IP 192.168.188.188.515 > 192.168.1.1.55786: P 6:7(1) ack 26202 win 8212
2008-04-18 10:38:51.540199 IP 192.168.188.188.515 > 192.168.1.1.55786: F 7:7(0) ack 26202 win 8212
2008-04-18 10:38:51.751202 IP 192.168.1.1.55786 > 192.168.188.188.515: R 2765892289:2765892289(0) win 32768
2008-04-18 10:38:51.751539 IP 192.168.1.1.55786 > 192.168.188.188.515: R 2765892289:2765892289(0) win 0

Best regards,
Holger Kipp