C# Socket send the [RST][ACK] package after [ACK] packager

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C#2.0

C#

192.168.1.152 is the Server
192.168.1.153 is the Client
Use TCP/IP protocol

the socket configed like this,both the Server and Client

socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);

Client connect to Server,and Server send the heartbeat packaget to Client.but the connect has the problem,

it occur after two days or a week or a month,so I use the Sniffer to get detail,
The results are as follows

Server->Client [PSH][ACk]
Client->Server [ACK]
Server->Client [PSH][ACk]
Client->Server [ACK]
Server->Client [PSH][ACk]
Client->Server [ACK]
.
.
.
Server->Client [PSH][ACk]
Client->Server [ACK]
Client->Server [ACK][RST]

Client ->Server[Three handshake]



where Client->Server [ACK][RST] come from and avoid