ACK and RST packets sent after successfully terminating TCP connection

[n j]

Hi all,

I'm reposting this from the freebsd-questions hoping for some answers.
I feel there is something wrong here, but would really appreciate a
second opinion before opening a bug report. The problematic part is
marked with [what is this?].

- in case of successful connection:

[begin handshake]
14:52:57.866040 IP client.example.net.6524 > server.example.net.9002:
S 813851098:813851098(0) win 8192 <mss 1380,nop,wscale
2,nop,nop,sackOK>
14:52:57.866057 IP server.example.net.9002 > client.example.net.6524:
S 3888621507:3888621507(0) ack 813851099 win 65535 <mss
1380,nop,wscale 3,sackOK,eol>
14:52:57.867143 IP client.example.net.6524 > server.example.net.9002:
. ack 3888621508 win 16560
[end handshake & begin data]
14:52:57.868333 IP client.example.net.6524 > server.example.net.9002:
P 813851099:813852180(1081) ack 3888621508 win 16560
14:52:57.967858 IP server.example.net.9002 > client.example.net.6524:
. ack 813852180 win 8144
14:53:35.533165 IP server.example.net.9002 > client.example.net.6524:
P 3888621508:3888621542(34) ack 813852180 win 8144
[end data & begin teardown]
14:53:35.564542 IP server.example.net.9002 > client.example.net.6524:
FP 3888621542:3888621675(133) ack 813852180 win 8280
14:53:35.566228 IP client.example.net.6524 > server.example.net.9002:
. ack 3888621676 win 16518
14:53:35.566289 IP client.example.net.6524 > server.example.net.9002:
F 813852180:813852180(0) ack 3888621676 win 16518
14:53:35.566318 IP server.example.net.9002 > client.example.net.6524:
. ack 813852181 win 8279
[end teardown]
[what is this?]
14:53:36.172081 IP server.example.net.9002 > client.example.net.6524:
. ack 813852180 win 0
14:53:36.172101 IP server.example.net.9002 > client.example.net.6524:
. ack 813852181 win 8279

- in case of unsuccessful connection:

[begin handshake]
14:53:00.411337 IP client.example.net.6547 > server.example.net.9002:
S 1055031875:1055031875(0) win 8192 <mss 1380,nop,wscale
2,nop,nop,sackOK>
14:53:00.411354 IP server.example.net.9002 > client.example.net.6547:
S 2849043653:2849043653(0) ack 1055031876 win 65535 <mss
1380,nop,wscale 3,sackOK,eol>
14:53:00.412242 IP client.example.net.6547 > server.example.net.9002:
. ack 2849043654 win 16560
[end handshake & reset connection]
14:53:00.412251 IP server.example.net.9002 > client.example.net.6547:
R 2849043654:2849043654(0) win 0
[what is this?]
14:53:01.168076 IP server.example.net.9002 > client.example.net.6547:
. ack 1055031876 win 0
14:53:01.168100 IP server.example.net.9002 > client.example.net.6547:
R 2849043654:2849043654(0) win 0
14:53:01.168393 IP client.example.net.6547 > server.example.net.9002:
R 1055031876:1055031876(0) ack 2849043653 win 0

The server is running 7.2 GENERIC.

Thanks,
--
Nino