title: Is there a TCP protocol violation causing "TCP connection lost" in these packets?
body: <p>I have narrowed down a failure in communications to the following exchange. I can see the TCP establishment SYN, SYN/ACK, and ACK packets starting at packet #74. 22ms later, the connection is reported lost (very near the PSH packet #77) and I can't understand why. Is it ACKing the wrong SEQ? Comms are over a PLC link if it matters. The .6232 address belongs to my side of the link.</p>
  
  <p>Many thanks in advance.</p>
  
  <p>The evidence:</p>
  
  <p>An EVSE communications controller (whose code I am not privileged to see) reports the following sequence of events:</p>
  
  <pre><code>[16/11/23_13:38:37:606] [Message] Sdp request successfully received and checked!
  [16/11/23_13:38:37:797] [Message] TCP connection established ...
  [16/11/23_13:38:37:801] [Message] Expected next Request: SupportedAppProtocol
  [16/11/23_13:38:37:819] [Message] TCP connection lost ...
  </code></pre>
  
  <p>with these packets tcpdump'ed from the same EVSE's network:</p>
  
  <pre><code>#71 13:38:37.603416 IP6 fe80::201:87ff:fe05:2cbf &gt; ff02::1:ff62:6232: ICMP6, neighbor solicitation, who has fe80::201:1ff:fe62:6232, length 32
      0x0000:  3333 ff62 6232 0001 8705 2cbf 86dd 6000  33.bb2....,...`.
      0x0010:  0000 0020 3aff fe80 0000 0000 0000 0201  ....:...........
      0x0020:  87ff fe05 2cbf ff02 0000 0000 0000 0000  ....,...........
      0x0030:  0001 ff62 6232 8700 4ce8 0000 0000 fe80  ...bb2..L.......
      0x0040:  0000 0000 0000 0201 01ff fe62 6232 0101  ...........bb2..
      0x0050:  0001 8705 2cbf                           ....,.
  #72 13:38:37.620216 IP6 fe80::201:1ff:fe62:6232 &gt; fe80::201:87ff:fe05:2cbf: ICMP6, neighbor advertisement, tgt is fe80::201:1ff:fe62:6232, length 32
      0x0000:  0001 8705 2cbf 0001 0162 6232 86dd 6000  ....,....bb2..`.
      0x0010:  0000 0020 3aff fe80 0000 0000 0000 0201  ....:...........
      0x0020:  01ff fe62 6232 fe80 0000 0000 0000 0201  ...bb2..........
      0x0030:  87ff fe05 2cbf 8800 389b 6000 0000 fe80  ....,...8.`.....
      0x0040:  0000 0000 0000 0201 01ff fe62 6232 0201  ...........bb2..
      0x0050:  0001 0162 6232                           ...bb2
  #73 13:38:37.620431 IP6 fe80::201:87ff:fe05:2cbf.15118 &gt; fe80::201:1ff:fe62:6232.56978: UDP, length 28
      0x0000:  0001 0162 6232 0001 8705 2cbf 86dd 6000  ...bb2....,...`.
      0x0010:  0000 0024 1140 fe80 0000 0000 0000 0201  ...$.@..........
      0x0020:  87ff fe05 2cbf fe80 0000 0000 0000 0201  ....,...........
      0x0030:  01ff fe62 6232 3b0e de92 0024 ac61 01fe  ...bb2;....$.a..
      0x0040:  9001 0000 0014 fe80 0000 0000 0000 0201  ................
      0x0050:  87ff fe05 2cbf cdec 1000                 ....,.....
  #74 13:38:37.784028 IP6 fe80::201:1ff:fe62:6232.56056 &gt; fe80::201:87ff:fe05:2cbf.52716: Flags [S], seq 7266836, win 3107, options [mss 1440], length 0
      0x0000:  0001 8705 2cbf 0001 0162 6232 86dd 6000  ....,....bb2..`.
      0x0010:  0000 0018 06ff fe80 0000 0000 0000 0201  ................
      0x0020:  01ff fe62 6232 fe80 0000 0000 0000 0201  ...bb2..........
      0x0030:  87ff fe05 2cbf daf8 cdec 006e e214 0000  ....,......n....
      0x0040:  0000 6002 0c23 ea52 0000 0204 05a0       ..`..#.R......
  #75 13:38:37.784415 IP6 fe80::201:87ff:fe05:2cbf.52716 &gt; fe80::201:1ff:fe62:6232.56056: Flags [S.], seq 206804358, ack 7266837, win 14400, options [mss 1440], length 0
      0x0000:  0001 0162 6232 0001 8705 2cbf 86dd 6000  ...bb2....,...`.
      0x0010:  0000 0018 0640 fe80 0000 0000 0000 0201  .....@..........
      0x0020:  87ff fe05 2cbf fe80 0000 0000 0000 0201  ....,...........
      0x0030:  01ff fe62 6232 cdec daf8 0c53 9586 006e  ...bb2.....S...n
      0x0040:  e215 6012 3840 1c4b 0000 0204 05a0       ..`.8@.K......
  #76 13:38:37.794237 IP6 fe80::201:1ff:fe62:6232.56056 &gt; fe80::201:87ff:fe05:2cbf.52716: Flags [.], ack 1, win 3107, length 0
      0x0000:  0001 8705 2cbf 0001 0162 6232 86dd 6000  ....,....bb2..`.
      0x0010:  0000 0014 06ff fe80 0000 0000 0000 0201  ................
      0x0020:  01ff fe62 6232 fe80 0000 0000 0000 0201  ...bb2..........
      0x0030:  87ff fe05 2cbf daf8 cdec 006e e215 0c53  ....,......n...S
      0x0040:  9587 5010 0c23 6011 0000                 ..P..#`...
  #77 13:38:37.810215 IP6 fe80::201:1ff:fe62:6232.56056 &gt; fe80::201:87ff:fe05:2cbf.52716: Flags [P.], seq 1:18, ack 1, win 3107, length 17
      0x0000:  0001 8705 2cbf 0001 0162 6232 86dd 6000  ....,....bb2..`.
      0x0010:  0000 0025 06ff fe80 0000 0000 0000 0201  ...%............
      0x0020:  01ff fe62 6232 fe80 0000 0000 0000 0201  ...bb2..........
      0x0030:  87ff fe05 2cbf daf8 cdec 006e e215 0c53  ....,......n...S
      0x0040:  9587 5018 0c23 ebbc 0000 01fe 8001 0000  ..P..#..........
      0x0050:  0009 809a 0010 1108 4080 20              ........@..
  #78 13:38:37.810533 IP6 fe80::201:87ff:fe05:2cbf.52716 &gt; fe80::201:1ff:fe62:6232.56056: Flags [.], ack 18, win 14400, length 0
      0x0000:  0001 0162 6232 0001 8705 2cbf 86dd 6000  ...bb2....,...`.
      0x0010:  0000 0014 0640 fe80 0000 0000 0000 0201  .....@..........
      0x0020:  87ff fe05 2cbf fe80 0000 0000 0000 0201  ....,...........
      0x0030:  01ff fe62 6232 cdec daf8 0c53 9587 006e  ...bb2.....S...n
      0x0040:  e226 5010 3840 33e3 0000                 .&amp;P.8@3...
  #79 13:38:37.814004 IP6 fe80::201:1ff:fe62:6232.56056 &gt; fe80::201:87ff:fe05:2cbf.52716: Flags [.], ack 1, win 3107, length 0
      0x0000:  0001 8705 2cbf 0001 0162 6232 86dd 6000  ....,....bb2..`.
      0x0010:  0000 0014 06ff fe80 0000 0000 0000 0201  ................
      0x0020:  01ff fe62 6232 fe80 0000 0000 0000 0201  ...bb2..........
      0x0030:  87ff fe05 2cbf daf8 cdec 006e e215 0c53  ....,......n...S
      0x0040:  9587 5010 0c23 6011 0000                 ..P..#`...
  #80 13:38:37.814310 IP6 fe80::201:87ff:fe05:2cbf.52716 &gt; fe80::201:1ff:fe62:6232.56056: Flags [.], ack 18, win 14400, length 0
      0x0000:  0001 0162 6232 0001 8705 2cbf 86dd 6000  ...bb2....,...`.
      0x0010:  0000 0014 0640 fe80 0000 0000 0000 0201  .....@..........
      0x0020:  87ff fe05 2cbf fe80 0000 0000 0000 0201  ....,...........
      0x0030:  01ff fe62 6232 cdec daf8 0c53 9587 006e  ...bb2.....S...n
      0x0040:  e226 5010 3840 33e3 0000                 .&amp;P.8@3...
  #81 13:38:37.817695 IP6 fe80::201:87ff:fe05:2cbf.52716 &gt; fe80::201:1ff:fe62:6232.56056: Flags [F.], seq 1, ack 18, win 14400, length 0
      0x0000:  0001 0162 6232 0001 8705 2cbf 86dd 6000  ...bb2....,...`.
      0x0010:  0000 0014 0640 fe80 0000 0000 0000 0201  .....@..........
      0x0020:  87ff fe05 2cbf fe80 0000 0000 0000 0201  ....,...........
      0x0030:  01ff fe62 6232 cdec daf8 0c53 9587 006e  ...bb2.....S...n
      0x0040:  e226 5011 3840 33e2 0000                 .&amp;P.8@3...
  </code></pre>