Zero window and RST

Hi Experts,

I am facing with the follwoving contradiction. In RFC 793 can be read the following sentences:

once: "all reset (RST) segments are validated by checking their SEQ-fields. A reset is valid if its sequence number is in the window."

on other part of the doc: "However, when the receive window is zero, a TCP must process the RST and URG fields of all incoming segments"

Which is "more" true?

My exact problem is, that I have to decide, and declare which device is wrong (a client or Cisco ACE). The problem begins, when the server (ACE) sends a FIN. The communication looks like this (client:100.1.1.7):

  1 19:30:57.486 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
  2 19:30:57.498 100.1.1.2             100.1.1.7             64    TCP      33067 > 51591 [SYN, ACK] Seq=0 Ack=1 Win=8192 Len=0 MSS=1460
  3 19:30:57.532 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [ACK] Seq=1 Ack=1 Win=4095 Len=0
  4 19:31:00.720 100.1.1.7             100.1.1.2             201   TCP      51591 > 33067 [PSH, ACK] Seq=1 Ack=1 Win=4095 Len=143
  5 19:31:00.781 100.1.1.2             100.1.1.7             64    TCP      33067 > 51591 [ACK] Seq=1 Ack=144 Win=8192 Len=0
  6 19:31:00.797 100.1.1.2             100.1.1.7             140   TCP      33067 > 51591 [PSH, ACK] Seq=1 Ack=144 Win=8192 Len=82
  7 19:31:00.800 100.1.1.2             100.1.1.7             64    TCP      33067 > 51591 [FIN, ACK] Seq=83 Ack=144 Win=8192 Len=0
  8 19:31:00.863 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [ACK] Seq=144 Ack=83 Win=4013 Len=0
  9 19:31:00.874 100.1.1.7             100.1.1.2             64    TCP      [TCP ZeroWindow] 51591 > 33067 [ACK] Seq=144 Ack=84 Win=0 Len=0
 10 19:31:04.381 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [RST] Seq=145 Win=0 Len=0
 11 19:31:04.382 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=84 Ack=144 Win=0 Len=0

The client doesn't replies normally to the FIN, it replies wit a simple ACK (#8), with unchanged ACK field. Furthermore it sends a zero window ACK (#9) where Ack+1. This window size shouldn't influence the server side rcv.wnd, which was 8192 in packet #6 and #7. Here comes the worst, that the server ignores the incoming (#10) RST packet (comes with Ack+1), and pretends like the sesion is still open. In the next message (#11) server sets zero window as well with seq=144) This is my question: should the server process this RST? What is the server side rcv.wnd size when the RST arrives, and if it were zero, shuld have process the RST if that has an out-of-window seq or not? (server ack=144+0 win.siz. incoming RST seq=145). This is a special communication, where the client and server uses fixed TCP src and dst ports, thus the client cannot re-estabilis a conn, until the server runs on timeout (several minutes).

The converstaion follows like this:

 12 19:42:14.450 100.1.1.7             100.1.1.2             64    TCP      [TCP Port numbers reused] 51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
 13 19:42:14.450 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=1 Ack=3592380271 Win=0 Len=0
 14 19:42:16.596 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
 15 19:42:16.596 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=1 Ack=3592380271 Win=0 Len=0
 16 19:42:18.622 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
 17 19:42:18.622 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=1 Ack=3592380271 Win=0 Len=0
 18 19:42:22.893 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
 19 19:42:22.893 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=1 Ack=3592380271 Win=0 Len=0
 20 19:42:30.896 100.1.1.7             100.1.1.2             64    TCP      51591 > 33067 [SYN] Seq=0 Win=0 Len=0 MSS=1400
 21 19:42:30.896 100.1.1.2             100.1.1.7             64    TCP      [TCP ZeroWindow] 33067 > 51591 [ACK] Seq=1 Ack=3592380271 Win=0 Len=0

etc.

Thank you for your help in advance.

BR: jonagy