INFO: How the SNA Server Client Chooses a "Sponsor" SNA Server

MORE INFORMATION

The client locates a sponsor server as follows:

• If Named Pipes or TCP/IP is configured on the SNA client, and the client is configured as local to the server(s), the client sends a broadcast to the subdomain and waits for a response from a server-side SnaBase service. The first SnaBase to respond to the client's request will be tried for the sponsor connection.
  
  NOTE: If the server is located on a different TCP/IP subnet than the client, this broadcast is normally filtered by any intermediate IP routers separating the client and server. In this configuration, the remote connection method should be chosen during SNA client setup.
• If the SNA Server 2.11 Service Pack 1 (or later) client software is being used on Windows 3.x, Windows 95 or Windows NT, the client will randomly choose a server from this list. However, the SNA Windows 3.x and Windows NT clients (and the Windows 95 client, with an update to SNA Server 3.0 post-SP1) can be configured to try servers in the order they're configured, by setting the RandomSponsor setting documented below. The MS-DOS client doesn't support TCP/IP sockets. When named pipes is chosen, the MS-DOS client tries the remote servers in order and never randomly chooses the sponsor server.
  
  NOTE: The SNA client Setup programs only prompt for two remote server names. To configure additional remote servers, they can be manually added for the Windows 3.x, Windows 95 and Windows NT clients as follows:
• Windows 3.x client: Add server names preceded with \\ on the Remote= line in the [WNAP] section of Win.ini, separating the server names with spaces. When connecting over TCP/IP, the server's IP address may be specified explicitly. For example:
  
  Remote= \\server1 \\server2 \\124.55.69.45
• Windows 95 client: add server names to the following registry value, separated by spaces, but *not* prepended with \\. For example:

  HKEY_LOCAL_MACHINE/Software/Microsoft/SnaBase/Parameters:
           Sponsors: server1 server2 server3
  						

• Windows NT client: add server names to the following registry value (servers must be listed on separate lines):

  HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/ 
        SnaBase/Parameters
            Sponsors: REG_MULTI_SZ: server1
                                    server2
                                    server3
  						

• If NetWare IPX/SPX is configured on the SNA client, and the client is configured as local to the server(s), the client queries the NetWare bindery based on the subdomain name entered during SNA client setup. The server-side SnaBase service automatically registers with the NetWare bindery, specifying the SNA subdomain name and a SAP service type of 0x444. The client retrieves all SNA Server computers from the bindery, and then randomly chooses a server.
• If NetWare IPX/SPX is configured on the SNA Windows 95 or Windows NT client, and the client is configured as remote to the server(s), the client queries the NetWare bindery looking for the specific server names specified during SNA client setup. The server names are stored in the registry as described earlier. The server-side SnaBase service automatically registers with the NetWare bindery and specify their subdomain name and a SAP service type of 0x444. The client locates the servers in the bindery, and then randomly chooses a server.
  
  NOTE: When connecting over Banyan or NetWare IPX/SPX, the SNA Server Windows 3.x client only supports local connection mode described earlier.
• If Banyan Vines is configured on the SNA Windows 95 or Windows NT client, the client queries the Banyan StreetTalk directory service based on the StreetTalk list name (that is, subdomain name) entered during SNA client setup. The server-side SnaBase service automatically registers with StreetTalk, creating a StreetTalk List based on the subdomain name, and a PC-based Service for each SNA Server. The client retrieves all SNA Server computers from the StreetTalk List, and then randomly chooses a server.

The sponsor connection must be successfully established before an SNA application session (that is, 3270, LUA, APPC, CPIC, CSV, and so forth) will connect to an SNA Server.

Background on the Sponsor Connection

When the SNA Server client software initializes, it opens a "sponsor" (or service) connection to the SnaBase service on an SNA Server in the subdomain. The following functions are performed over this sponsor connection:

• The client is notified of SNA Server computers running in the subdomain.
• The server responds to various client requests, including requests for 3270 user/group records.
• When connecting over TCP/IP sockets, NetWare IPX/SPX or Banyan Vines, the SnaBase service performs a Windows NT domain log on for the client.
• The client notifies the server of any autostarted invokable TPs that are registered on the client computer. The server sends dynamic load requests to the client when an attach request is received, if the invokable TP is configured on the client.
• The client reports errors to the server, to write to the Windows NT application event log.

The RandomSponsor Setting

The SNA Server 2.11 Service Pack 1 (or later) client software implements random selection of a sponsor server if Named Pipes or TCP/IP is configured with the remote option. The initial release of SNA Server 2.11 and previous versions of the SNA client software will open remote sponsor servers in the order configured.

By randomly choosing a sponsor server, the SNA Windows 3.x, Windows 95 and Windows NT clients will tend to load balance across SNA Servers for their sponsor connection to help distribute the load across servers.

The RandomSponsor setting can be configured for the Windows 95 client after applying SNA Server 3.0 Service Pack 2. If this Service Pack is not applied, remote sponsor servers are always tried in random order.

The RandomSponsor setting is enabled by default for Windows 3.x, Windows NT, and Windows 95 clients but can be disabled through the following configuration setting:

SNA Server Windows 95 Client

If the SNA Server 3.0 Service Pack 2 Windows 95 client is applied, the following entry may be set:

   HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/SnaBase/Parameters/ 
   RandomSponsor: 0
				

SNA Server Windows 3.x (or WFW) Client

In the [WNAP] section of Win.ini:

   RandomSponsor = NO
				

SNA Server Windows NT Client

   HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/SnaBase/Parameters/ 
   RandomSponsor: REG_DWORD: 0
				

The client SnaBase service must be restarted to implement this change.

Disabling the RandomSponsor setting causes the SNA client to try the remote servers in the order they're configured.