Algorithm Used to Accept Requests from SNA Devices

• Microsoft SNA Server for Windows NT, versions 2.0, 2.10, 2.11, and 3.0

SUMMARY

This article explains how SNA Server uses identifying information (XIDs) from incoming calls to help you decide which kind of remote node identifier to specify for a connection that accepts incoming calls.

MORE INFORMATION

When SNA Server receives an XID from an incoming call such as a DSPU, host, or AS/400, for instance, it looks at the XID for some kind of identifier of the remote system that made the call. It compares this identifier, in the order shown in the following list, against identifiers stored in the SNA Server configuration. If it finds a match, it accepts the call. If it finds that identifiers are left unspecified (in the configuration and/or the XID), and the connection is an SDLC connection, SNA Server accepts the call, pending further exchange of information. In other cases, if every comparison yields a mismatch, or when identifiers are left unspecified and the connection is 802.2 or X.25, SNA Server rejects the incoming call.

Identifiers are compared in the following order:

1. If the incoming XID is Format 3, SNA Server examines the XID for a remote node Network Name and Control Point Name. If these parameters are present in both the incoming XID and in the SNA Server configuration, and they match, the call is accepted. If the parameters are present and do not match, the call is rejected.

2. If the parameters are not available for the preceding step, Remote Node IDs are examined next. Remote Node IDs may be used in either Format 0 or Format 3 XIDs. If a Remote Node ID is present in both the incoming XID and in the SNA Server configuration, and they match, the call is accepted. If the parameters are present and do not match, the call is rejected.

3. If the parameters were not available for the preceding steps, for 802.2 and X.25 connections, remote addresses are examined:

       - For 802.2 connections, the Remote Network Address in the SNA Server
         configuration is compared to the address from which the XID was
         received. If the addresses match, the call is accepted; if not, the
         call is rejected.
   

         NOTE: SNA Server 2.11 has a new feature that allows any client to
         attach to SNA Server regardless of an XID or remote network address
         match. To do this, configure the downstream connection's remote
         network address to be: 400000000000.
   

       - For X.25 connections, the remote X.25 address in the SNA Server
         configuration is compared to the address from which the XID was
         received. If the addresses match, the call is accepted; if not, the
         call is rejected.
   

4. If no match is found in any of the preceding steps:

       - For 802.2 and X.25 connections the incoming call is rejected.
   

       - For SDLC connections, if identifiers were left unspecified in the
         configuration and/or the XID, the call is accepted, pending further
         exchange of identifiers. However, if identifiers were not left
         unspecified and no identifiers match, the call is rejected.
   

To Enable Incoming Calls for a Specific Connection

For 2.11:

1. In SNA Server Admin, go to Connection Properties for the specific connection.

2. Select Allowed Directions: Incoming Calls.

1. In SNA Server Manager, go to the properties page of the connection in question.

2. In the General tab, select Allowed Directions: Incoming Calls.