["Andy Low" <list@xxxxxxxx>]

Hi,

Hope that someone can assist.

I have 3 hosts (host A, host B and host C). Host A is running some kind of
service at port 2000 and we suspect that the service lock certain files and
do not allow Host B to access. Host C is scheduled to download the same
files from Host A daily.

All the while, Host B has no problem connecting to Host A port 2000 except
when timing coincides with Host C downloading time.

I have used Ethereal at the scheduled time when Host C download data from
Host A and the result is below:

1) Host B --> Host A,    src port:1878    dst port: 2000
[SYN]    Seq=0    Ack=0    Win=16384    Len=0    MSS=1460

2) Host A --> Host B,    src port: 2000,    dst port: 1878
[SYN, ACK]    Seq=0    Ack=1    Win=8192    Len=0    MSS=536

3) Host B --> Host A,
[TCP ZeroWindow]    src port:1878    dst port:2000    [RST]
Seq=1    Ack=1576600895    Win=0    Len=0

If Host A lock the files ( I guess), why Host B sent RST packet to Host A?
Shouldn't Host A reject the connection? It seems like Host B initiate the
termination. Does it mean the problem is at Host B. Is RST packet always go
with TCP ZeroWindow?

Hope I am clear with my explanation.

Thanks,

Andy