How SNA Server Communicates with Other SNA Server Computers

• Microsoft SNA Server for Windows NT, versions 2.0, 2.1, 2.11, 2.11 SP1, and 3.0

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SUMMARY

SNA Server uses broadcasts to propagate its Service Table updates to other SNA server computers in the domain. This is necessary to keep all SNA Server computers abreast of any configuration change that is made or any action that is being taken in the SNA Server domain. SNA Server version 2.1 and later provides choices that allow an administrator of an SNA Server network to optimize the way this Service Table propagation occurs. This article should be read as a supplement to the Server Broadcasts dialog box Help file that can be launched from within the Server Broadcasts dialog box.

MORE INFORMATION

SNA Server 2.0

By default, SNA Server 2.0 sends broadcasts using the following method:

- WriteFile API call:

SNA Server uses a WriteFile API call to send broadcasts to other SNA Server computers in the domain. It does this by submitting a WriteFile API call that is sent in turn over all network protocols that the Workstation Service is bound to. For instance, if the Workstation Service is bound to NetBEUI, TCP/IP, and NWLink NetBIOS, SNA Server sends MailSlot broadcasts over all three of these protocols. Sending MailSlot broadcasts over all transports is a function of the WriteFile API call. This may cause unnecessary network traffic, however. In SNA Server 2.0, there is no way to disable this other than to remove unnecessary protocols from the Network applet in Control Panel.

- IPX Sockets if NWLink is installed:

If NWLink is installed, SNA Server 2.0 will send a mailslot broadcast over NWLink NetBIOS as described above, using the WriteFile API AND over a well- known IPX socket.

- TCP/IP MailSlots:

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For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

If the SNA Server computers are divided by TCP/IP routers, then enable the following registry parameter:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Snabase\Parameters\
   : EnableIPMailSlots:REG_SZ:YES

- For Comm Server Support:

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For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

By default, SNA Server 2.0 has turned on support for Comm Server Gateways, sending specific MailSlot broadcasts that they can recognize. If there are no Comm Server computers in the domain, add the following value to:

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Snabase\Parameters\
   : CommServerSupport:REG_SZ:NO

SNA Server 2.1, 2.11, and 2.11 SP1

SNA Server Admin enables the user to choose how two or more SNA Server computers communicate with each other. Go to the Server Broadcasts dialog box under the Options menu in SNA Server Admin. This dialog box includes the following choices:

   - Microsoft Networking
   - Novell NetWare (IPX/SPX)
   - Banyan Vines/IP
   - Windows Sockets (TCP/IP)
   - Router Server Broadcasts over IP routers

   - SNA Server 2.0 servers in the same domain
   - DCA/Microsoft Comm Server Client Support

When you select the “Microsoft Networking” option only, SNA Server versions 2.1, 2.11, and 2.11 SP1 send MailSlot broadcasts using the WriteFile API, just as SNA Server 2.0 does by default. SNA Server does this by submitting a WriteFile API call that is sent in turn over all network protocols that the Workstation Service is bound to. For instance, if the Workstation Service is bound to NetBEUI, TCP/IP, and NWLink NetBIOS, SNA Server sends MailSlot broadcasts over all three of these protocols. Sending MailSlot broadcasts over all transports is a function of the WriteFile API call. This may cause unnecessary network traffic, however.

- Native Transport Interface:

Unlike 2.0, SNA Server versions 2.1, 2.11, and 2.11 SP1 have options that enable the user to choose to send over selected native transports instead of using the WriteFile API call. These other choices are:

   - Novell NetWare (IPX/SPX)
   - Banyan Vines/IP
   - Windows Sockets (TCP/IP)

- Comm Server Support:

If there are no DCA/Microsoft Comm Server clients or servers, disable the following Comm Server Support options: "SNA Server 2.0 servers in the same domain" and "DCA/Microsoft Comm Server Client Support".

Clearing these values will reduce broadcast traffic by nearly one-half.

- TCP/IP MailSlots:

When SNA Server computers are separated by TCP/IP routers, select "Route Server Broadcasts over IP routers" if there is an IP router separating SNA Server computers. This is equivalent to setting EnableIPMailslots to YES under 2.0. As in 2.0, SNA Server will send MailSlot broadcasts to domain controllers in the domain over TCP/IP only, even though other protocols may be installed. For this configuration, SNA Server computers must be installed on primary or backup domain controllers. If the SNA Server computers do not reside on a domain controller with this option chosen, no SNA Server computer will “listen” for these MailSlots. Note: This option can only be chosen if “Microsoft Networking” is chosen.

SNA Server 3.0

SNA Server Manager enables you to choose how two or more SNA Server computers communicate with each other. Go to the Server Broadcasts tab under the Properties page for the SNA Server Subdomain in SNA Server Manager. The Server Broadcasts tab includes the following choices:

   - Microsoft Networking (Named Pipes)
   - IPX/SPX (Novell NetWare)
   - TCP/IP
   - Banyan Vines

When you select only the "Microsoft Networking" option, SNA Server 3.0 sends MailSlot broadcasts using the WriteFile API, just as the previous versions of SNA Server do by default. Version 3.0 does this by submitting a WriteFile API call that is sent in turn over all network protocols that the Workstation Service is bound to. For example, if the Workstation Service is bound to NetBEUI, TCP/IP, and NWLink NetBIOS, SNA Server sends MailSlot broadcasts over all three of these protocols. Sending MailSlot broadcasts over all transports is a function of the WriteFile API call. This may cause unnecessary network traffic, however.

- Native Transport Interface:

SNA Server 3.0 has options that enable you to choose to send over selected native transports instead of using the WriteFile API call. These other choices are:

   - IPX/SPX (Novell NetWare)
   - TCP/IP
   - Banyan Vines

- TCP/IP MailSlots:

Unlike previous versions of SNA Server, SNA Server 3.0 does not have a "Route Server Broadcasts over IP routers" option. With SNA Server 3.0, each SNA Server computer builds a list of other SNA Server computers in its subdomain. The list of servers is built based on the current SNA Server configuration file. During installation, the SNA Server 3.0 Setup program tries to dynamically locate the primary SNA Server computer, based on a UDP broadcast datagram. If this fails, the Setup program displays a prompt asking for the primary SNA Server computer's name. Backup SNA Server computers store in their registry the name of the primary SNA Server computer. Member SNA Server computers store in their registry the names of all of the SNA Server computers in their subdomain.

Due to this change, SNA Server 3.0 does not have to be installed on Windows NT domain controllers even if the subdomain spans IP routers.

Additional query word: prodsna

Keywords          : snaadmin snamanager snasetup kbnetwork
Version           : Windows:2.0,2.1,2.11,3.0
Platform          : WINDOWS
Issue type        : kbinfo