DLC May Fail When Connecting Through an IBM 2210 Router (168662)

SYMPTOMS

With a data link control (DLC) connection established to a mainframe over an IBM 2210 router on a slow network, the network communication fails between the mainframe and the Microsoft DLC client.

CAUSE

When the IBM 2210 router is operating on a slow network there is a possibility that the receive buffer for the router (the receiving station) will fill up. Under these conditions, the IBM 2210 router will send two LLC packets to the Microsoft client (the sending station), a Receiver Not Ready (RNR) which indicates that the last Information Frame (I-Frame) packet was received from the sending station and that the receiving station is temporarily unavailable. Then the sending station sends a Receiver Ready (RR) for the same sequence packet that it had previously acknowledged with a RNR frame. This causes a problem in the Microsoft DLC stack because our client is not expecting two acknowledgements for the same I-Frame packet.

MORE INFORMATION

If you look at a network trace of this problem, you will see a RNR message from the router immediately followed by a RR message. The Microsoft client will send a frame reject (FRMR) message followed by a disconnect (DISC) message.

1.  RNR DSAP=0x04 SSAP=0x05 R N(R) = 0x2A FINAL  - Router
2.  RR DSAP=0x04 SSAP=0x04 C N(R) = 0x2B  - Router
3.  FRMR DSAP=0x04 SSAP=0x05 R FINAL - Client
4.  DISC DSAP=0x04 SSAP=0x04 C POLL - Client
5.  DISC DSAP=0x04 SSAP=0x04 C POLL - Client
6.  DISC DSAP=0x04 SSAP=0x04 C POLL - Client

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.51. A supported fix is now available, but has not been fully regression- tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.