TN3270 Server Rejects Client Model Types

• Microsoft SNA Server for Windows NT, version 2.11

SYMPTOMS

If your TN3270 clients are configured with two LU pools, each with different 3270 LU Model types, a TN3270 client is only able to connect with one Model type.

Steps To Reproduce Problem

1. Use TN3270 Server Admin to set up two pools or use individual LU's:

        Pool1 use Model 2
        Pool2 use Model 5
   

2. Try to connect.

   NOTE: Only the Model 5 clients are able to connect in this example.

CAUSE

When the TN3270 client accesses an LU for the first time, the TN3270 server starts an LU list of LUs that the client may access, however, when the client tries to connect to another LU, the TN3270 server fails to add that LU to the LU list, thus always limiting the client to the first LU.

RESOLUTION

Microsoft has updated the following file to correct this problem:

   <tnserverroot>\TN3SERVR.EXE

STATUS

Microsoft has confirmed this to be a problem in SNA Server for Windows NT. This problem was corrected in the latest SNA Server for Windows NT, 2.11 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K

MORE INFORMATION

The problem lies in the TN3270 Server implementation of TCP/IP masking. Each LU configured for use by the TN3270 Server can have TCP/IP masks associated with it, and these masks specify the TCP/IP addresses of clients that may connect through that LU. By default each LU has a mask that lets any client connect. When a client first tries to connect (and this is before the client has specified which Model type it wants to use) the server builds a list of LUs that that client may access, based on the LU's TCP/IP mask and the client's TCP/IP address.

In the Steps To Reproduce Problem example above, there are two LUs configured, one that supports Model 2 requests and one that supports Model 5 requests. When the client tries to connect, the server builds the list of LUs and stops when it has that one LU in the list. When the client tries to connect again the LU it selects is always the one that supports Model 5 requests. When the client requests a Model 2 terminal, the server rejects the request, because the only LU in the list is a Model 5 LU.