IIS 8.5 Windows 2012 R2 - RST ACK problem question

hello,

we are searching for any hints or solutions.

What happend ? The Webserver Application "asks" the server 123.123.123.123 (which is outside from our networks) and gets an response. (Authentication of an user / password)

normally is see this messages:

8530 1540.845929000 10.42.1.155 123.123.123.123 TLSv1 507 Application Data 8533 1540.898016000 10.42.1.155 123.123.123.123 TCP 54 52471→443 [ACK] Seq=49453 Ack=770885 Win=782080 Len=0

but very often we got these, not periodic... :

"265","146.538402000","10.42.1.155","123.123.123.123","TCP","54","52420 > 443 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0" "892","223.904937000","10.42.1.155","123.123.123.123","TCP","54","52408 > 443 [RST, ACK] Seq=35119 Ack=636018 Win=0 Len=0"

Transmission Control Protocol, Src Port: 52477 (52477), Dst Port: 443 (443), Seq: 751, Ack: 1088, Len: 0 .... 0000 0001 0100 = Flags: 0x014 (RST, ACK) .... .... .1.. = Reset: Set Expert Info (Warn/Sequence): Connection reset (RST)

and maybe this is related to the error messages in our application log:

ERR 530536125 26.08.2014 10:19:21 Unable to read data from the transport connection: The connection was closed. ERR 530535312 26.08.2014 10:19:21 System.IO.IOException: Unable to read data from the transport connection: The connection was [email protected]
at System.Net.ConnectStream.Read(Byte[] buffer, Int32 offset, Int32 size)@ at System.IO.StreamReader.ReadBuffer()@ at System.IO.StreamReader.ReadToEnd()@ at syo2redir.ovvRedirector.ProcessRequest(String URL, HttpRequest Request)

I cant find a reason why.. Any ideas ?