How To How SNA Server Communicates with Other SNA Server Computers (123337)

SUMMARY

Microsoft SNA Server 4.0 and Microsoft Host Integration Server 2000 use broadcasts to propagate their Service Table updates to other SNA server and Host Integration Server 2000 computers in the domain. This behavior is necessary to keep all SNA Server and Host Integration Server 2000 computers aware of any configuration change that is made or any action that is being taken in the SNA Server domain. With SNA Server version 4.0 and Host Integration Server 2000, an administrator of an SNA Server network can optimize the way that this Service Table propagation occurs.

Read this article as a supplement to the Help file that can be launched from within the Server Broadcasts dialog box.

MORE INFORMATION

SNA Server 4.0 SP4 , Host Integration Server 2000, and Host Integration Server 2000 SP1

With SNA Server Manager, you can choose how two or more SNA Server or Host Integration Server 2000 computers communicate with each other. Click 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
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Microsoft Networking

When you select only the Microsoft Networking option, SNA Server 4.0 and Host Integration Server 2000 send MailSlot broadcasts using the WriteFile API, just as the earlier versions of SNA Server do by default. SNA Server 4.0 and Host Integration Server 2000 do 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 and Host Integration Server 2000 send MailSlot broadcasts over all three of these protocols. Sending MailSlot broadcasts over all transports is a function of the WriteFile API call. However, this action may cause unnecessary network traffic.

Native transport interface

Options in SNA Server 4.0 and Host Integration Server 2000 allow you to choose to send over selected native transports instead of using the WriteFile API call. These other choices are the following:

IPX/SPX (Novell NetWare)
TCP/IP
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For example, if TCP/IP is installed on all SNA Server and Host Integration Server 2000 computers, you want to clear "Microsoft Networking" and select "TCP/IP". This reduces the number of MailSlot broadcasts by sending over only one transport. In this case, the transport is TCP/IP.

TCP/IP MailSlots

Unlike earlier versions of SNA Server, SNA Server 4.0 and Host Integration Server 2000 do not have a Route Server Broadcasts over IP routers option. With SNA Server 4.0 and Host Integration Server 2000, each SNA Server computer builds a list of other SNA Server or Host Integration Server 2000 computers in its subdomain. The list of servers is built based on the current SNA Server or Host Integration Server 2000 configuration file. During installation, the SNA Server 4.0 and Host Integration Server 2000 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 prompting for the name of the primary SNA Server computer. Backup SNA Server and Host Integration Server 2000 computers store in their registry the name of the primary SNA Server 4.0 and Host Integration Server 2000 computer. Member SNA Server computers (not an option in Host Integration Server 2000) store in their registry the names of all the SNA Server computers in their subdomain.

Because of this change, you do not have to install SNA Server 4.0 and Host Integration Server 2000 on Windows NT domain controllers even if the subdomain spans IP routers.