Connection Attempt Reset When Connecting to DOS Socket Server

• Microsoft LAN Manager, version 2.2c

SYMPTOMS

The attempt to connect to a Socket server application fails. The use of a network analyzer confirms that the Socket server is resetting every attempt to initiate the TCP connection.

CAUSE

A previous failure to establish a TCP Connection has occurred on the DOS Socket Server. The DOS Sockets driver believes that its backlog of listening connections is full and refuses attempts to establish new connections.

Every socket application must set the number of backlog (pending) connections the application supports. When a client attempts to connect to the server port (for example: A SYN packet is sent), the DOS Sockets driver increments the BACKLOG counter. When the connection has been accepted by the socket application, the BACKLOG counter is decremented. If the BACKLOG counter equals the maximum backlog the application is using (typically 1 for DOS Socket Server applications), then the DOS Socket driver silently refuses new connection requests (silent means that the Socket application is not informed of connection refusal). There exists a problem in the DOS Socket driver where it does not decrement the BACKLOG counter when a SYN packet has been received by a client, but an ACK from the client has not been received from the server's SYN-ACK.

Normal connection establishment appears as follows:

   CLIENT -> SERVER     SYN
   SERVER -> CLIENT     SYN-ACK
   CLIENT -> SERVER     ACK   (Missing) 

WORKAROUND

To work around this problem, stop the DOS Socket Server application and restart it periodically.

STATUS

Microsoft has confirmed this to be a problem in LAN Manager version 2.2c. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

Additional query words:

Keywords :
Version : :2.2c
Platform : MS-DOS
Issue type :