TN3270 LU Assignment and the Use of Submasks

• Microsoft SNA Server for Windows NT, versions 2.11 and 2.11 Service Pack 1

SUMMARY

When an IP subnet mask is defined in TN3270 Admin for an LU resource, the SNA Server 2.11 Service Pack 1 TN3270E Server checks the range of addresses used by the subnet mask to determine if a TN3270 user has access to the LU.

For example,

1. Add four LUA LUs to the TN3270E configuration.

2. Use any text editor to modify the Tn3270E configuration file (<tnroot>\Tnsvrcfg.tnc).

3. Define Three of the LUs with a class B ip address of 130.9.x.x and subnet mask of 255.255.0.0.

4. Define one LU with an address of 130.8.8.1 and subnet mask of 255.255.0.0.

   LU3 assigned to 130.9.5.1
   LU2 assigned to 130.9.5.2
   LU4 assigned to 130.9.8.1
   LU5 assigned to 130.8.8.1

   [Group 1]
   Name=LU3
   Comment=
   SNAResource1=LU3
   IPConnection1=130.009.005.001,255.255.000.000,00000,65535

MORE INFORMATION

When a client tries to connect to the server, the IP address of the client is masked (bitwise AND) by the subnet mask of each resource. The result from this mask is compared to the result from masking the subnet mask of the resource by the IP address configured for the resource.

The default subnet mask is 255.255.255.255. When this is used as a mask value it has no effect; therefore, in this case, when a client connects the IP address of the client is compared to the IP address configured for the resource.

In the example, the subnet mask is 255.255.0.0. When this is used as a mask, it makes the final two octets in the masked result zero. Therefore, in this case, a client that has the address 130.9.5.1 will be able to connect to any resource that has the configured IP address of 130.9.xxx.xxx, if that resource's mask is 255.255.0.0.