One of the important contributing factors fueling the growing popularity of Windows NT Server in the enterprise environment is its capability to provide connectivity to IBM AS/400 mid-range computers and IBM S/390 mainframes. Windows NT Server supports IBM host connectivity through Microsoft SNA Server, a member of the Microsoft BackOffice Suite. Microsoft SNA Server is a software gateway that runs on a Windows NT Server system to provide IBM host connectivity for the client PCs that are on the network.
Using Microsoft SNA Server for IBM host connectivity provides several benefits over directly connecting all of the PCs on your network to the IBM host. The network nodes need to support only the LAN protocol (TCP/IP, NetBEUI, IPX/SPX) that is required to connect to the network. They do not need to run the more resource-intensive SNA protocol that's normally required for IBM host connectivity in addition to the LAN protocol. The gateway can be managed from a central location, and you don't need to manually set up and configure every single system that requires host access. Users and groups can be authorized to or restricted from IBM host access by using SNA Server's management functions.
Microsoft SNA Server software can run either on the same system as the NT file server, or it can run on a dedicated communication server. The network nodes communicate with the SNA Server system by using a LAN-based protocol such as TCP/IP, NetBEUI, or IPX/SPX. The SNA Server system communicates to the AS/400 by using an SNA connection. Figure 51.1 provides an overview of an SNA Server connection to an IBM host.
This is an overview of SNA Server-to-host communications.
As you can see in Figure 51.1, the networked PCs use the LAN protocol to communicate with the SNA Server system. The SNA Server system, in turn, communicates to the IBM host by using the SNA protocol. The SNA Server can communicate with the IBM by using a separate connections/network connection, as shown in Figure 51.1, or it can communicate with the IBM host over the same network that is used by the client systems.
SNA Server uses a modular architecture that enables it to be used with a wide variety of network topologies, network protocols, and host connections. Figure 51.2 shows the modular architecture used by both the SNA Server system itself and the SNA Server client.
SNA Server is implemented by using an open driver interface, called SNADIS, which enables it to use almost all of the popular communications adapters. Overall, there are more than 90 different LAN and WAN communications adapters that SNA Server supports. SNA Server can connect to an IBM S/390 using a Channel attachment, 802.2 Ethernet or Token-Ring, Distributed Link Service, Coaxial DFT, SDLC, and X.25. SNA Server can connect to an IBM AS/400 using 802.2 Ethernet or Token-Ring LAN, Twinaxial, SDLC, and X.25.
In conjunction with the wide variety of communications adapters that it supports, SNA Server has protocol independence, which enables SNA Server to provide host connectivity for PC clients over a variety of different LAN protocols. SNA Server supports client connections using IPX/SPX, native TCP/IP, Named Pipes (over NetBEUI, RAS or TCP/IP), AppleTalk, and Banyan VINES IP. Protocol independence enables SNA Server to be used on more than just NT Server-based networks. For instance, SNA Server can provide host connectivity for NetWare and UNIX LANs, as well as Windows NT Server-based networks.
SNA Server achieves network and protocol independence by using a layered architecture.
On the client side, SNA Server provides support for a wide range of SNA protocols. For IBM mainframe connectivity, SNA Server supports LUA applications, which can use either the LUA/SLI or LUA/RUI protocols to access these data streams, as well as 3270 connectivity over the 3270 EIS API. For AS/400 connectivity, SNA Server supports host connectivity via the APPC API. SNA Server's APPC supports 5250 display emulation and EHNAPPC client/server applications, as well as CPI-C client/server applications. In addition, the ODBC support provided by SNA Server can provide host database integration to any ODBC-enabled desktop application, including Microsoft Office 97, Lotus SmartSuite, and many others.
Although the specific requirements vary depending on actual usage, in general terms, an Intel Pentium with 24M of memory is enough to deal with most low to moderate connection requirements. For higher needs, or if you simply don't want to be bothered with tuning the system, make sure that the SNA Server has at least 32M of memory, which is enough to handle high levels of SNA activity.
As with other native Windows NT applications, SNA Server uses a flat memory model, and it can take advantage of all of the real memory that is required by the application. If the application requirements exceed the amount of physical memory in the system, Windows NT will use virtual memory, paging the least-used sections of memory to the hard disk.
The built-in Performance Monitor can help determine the actual system requirements. Because its is based on the Windows NT operating systems, SNA Server is portable to platforms other than Intel-based systems. If additional processing power is required by the gateway system, SNA Server can also run on multiple CPU Intel systems, the DEC Alpha and MIPS RISC systems.
SNA Server's actual system requirements vary depending on the number of users and the type of host access and user activity being performed. The main variables that affect SNA Server's hardware requirements are:
Table 51.1 lays out some general guidelines for sizing SNA Server systems.
| Users | User Activity Level | System Requirements |
| 25 | Heavy | 486/33 with 32M RAM |
| 50 | Light-Moderate | 486/33 with 32M RAM |
| 200 | Heavy | 486/66 with 32M RAM |
| 500 | Light-Moderate | 486/66 with 32M RAM |
| 600 | Heavy | Pentium 133 with 64M RAM |
| 1500 | Light-Moderate | Pentium 133 with 64-128M RAM |
| 1500+ | Pentium Pro, SMP, or DEC Alpha with 64-128M RAM |
A more powerful CPU might be required if the Windows NT Server is performing double duty as a file server. In addition, as the number of clients passes 200, adding additional network adapters could improve the performance the SNA Server provides to clients.
TIP: If you have more than 300 connections, you should strongly consider running a second SNA Server to get load balancing and hot backup.
You install SNA Server by running the SETUP.EXE program from the SNA Server CD. As with other Windows NT applications from Microsoft, there are separate setup programs for Intel PC, DEC Alpha, IBM Power PC, and MIPS systems. There's a different CD subdirectory for each processor type:
| Processor | Installation Directory |
| Intel | \i386 |
| MIPS | \mips |
| DEC Alpha | \alpha |
| PowerPC | \ppc |
To install the Intel version, you need to run setup.exe from the i386 subdirectory. To run the SNA Server setup.exe program, you must be logged on to the Windows NT Server as a member of the Administrators group. The setup program creates a domain user account and modifies the Windows NT Server Registry. Installation of SNA Server requires a system with a minimum of 16M of RAM and 38M of free disk space.
During the installation, specify the information described in Table 51.2.
| Item | Description |
| Destination directory | The SNA Server directory is the folder on the Windows NT Server system that will contain the SNA Server application. |
| SNA Server components | The SNA Server components enable you to specify which SNA Server program components and Link Services will be installed. |
| Host Link Services | Essentially, the link services that are selected define the physical connection to the IBM host. |
| SNA Server licensing mode | The licensing mode enables you to select between per-server licensing, specifying a given number of network clients, and per-seat licensing, indicating a number of concurrent users. If you select per-server licensing, you have the option of later changing it to per-seat. If you select per-seat licensing, however, you cannot switch to per-server without reinstalling SNA Server. |
| SNA Server role | The SNA Server role indicates whether the SNA Server system is a Primary configurations server, a Backup configuration server, or a Member server. Primary and Backup servers maintain copies of the SNA Server configuration file, whereas Member servers don't. The Backup server maintains a read-only copy that becomes active only in the event of a failure of the Primary SNA Server. If you install only one SNA server system, specify that it is a Primary server. |
| SNA Server subdomain | An SNA Server subdomain provides finer control over hot backup and load balancing when SNA Server is installed in a large single domain environment by enabling the domain to be divided into smaller groups. |
After the setup is complete, you can configure SNA Server by running the SNA Server Manager. The SNA Server Manager shown in Figure 51.3 is SNA Server's graphical configuration and management application.
Use the SNA Manager for configuring and managing SNA Server.
The SNA Server configuration is a two-part process. First, you must manually configure a Link Service that describes the physical communications link to the AS/400. For instance, a link service might describe an 802.2 LAN connection, a twinaxial connection, an SDLC connection, or any of the other host connection types that are supported by SNA Server.
After the link service is configured, you can use one of the Configuration Wizards to configure a new 3270 connections or a new AS/400 connection. In the next section, you step through an example AS/400 configuration that uses the SNA Server Manager and the AS/400 Configuration Wizard.
You configure a link service by selecting the SNA Service entry in the Servers list box. There are two methods to add a new link service:
Either method causes the Insert Link Service dialog box shown in Figure 51.4 to appear.
Add a link service to define the physical connection to the AS/400.
The link services that you selected during the SNA Server installation appear in the Insert Link Service dialog box, which list only the link services that were previously installed. If you require a link service that's not listed in the Insert Link Service dialog box, you must rerun the SNA Server Setup program and select the missing Link Service in the SNA Server Components dialog box.
In Figure 51.4, you can see that the 802.2 Link Service is the only link service that appears in the Insert Link Services dialog box because it was the only option that was previously installed on this example system. Many other Link Services are available, including SDLC, X.25, Twinax, DFT, Channel, and others. Before adding an 802.2 Link Service, you must have installed the Microsoft DLC protocol on your Windows NT Server by using the Network Control Panel. After selecting the 802.2 Link Service and clicking the Add button, the 802.2 Link Service Properties dialog box shown in Figure 51.5 appears.
Select the link service for the SNA Server-to-host connection.
The main purpose of the 802.2 Link Service Properties dialog box is to specify the Link Service name that SNA Server will use. Because SNA Server can use multiple host links, each configured link service requires a unique name. The example in Figure 51.5 uses the default Link Service name DLC 802.2 Link Service #1.
In addition to the link service name, the 802.2 Link Services Properties dialog box also enables you to specify the physical adapter that you want to use with this Link Service, as well other link configuration properties. For instance, to configure an 802.2 Link service, you must indicate the SAP (Source Access Point) that will be used. The choice of network adapter and SAP value are only used when you have multiple network adapters in your SNA Server system. If you are using multiple adapters, then each adapter must use a unique SAP. The 802.2 Link Service configuration enables you to specify which adapter will be used by this link service and the SAP that it will use.
The next step in configuring SNA Server to connect to the AS/400 is to use the AS/400 Configuration Wizard. The AS/400 Configuration Wizard is started from the Tools menu of the SNA Server Manager. The Wizard displays a series of dialog boxes that guide you through the SNA Server configuration process, helping you specify the AS/400 connection properties, as well as the local and remote LU configurations. Selecting the Configure AS/400 option starts the Wizard (see Figure 51.6).
This figure shows you the Configuration Wizard.
Clicking the Next button begins the connection configuration process and displays the AS/400 Configuration Wizard shown in Figure 51.7.
Select the SNA Server to configure.
The SNA Server selection drop-down list box shown in Figure 51.7 enables you to select the SNA Server system to configure. By default, the local SNA Server system appears in the edit box portion of the drop-down list. As you can see in the example configuration shown in Figure 51.7, the Configuration Wizard used the local SNA Server of TECA2, which is the same name as the Windows NT Server system on which SNA Server was running.
After selecting the SNA Server system to configure, clicking the Next button moves you to the next SNA Server Configuration Wizard window, as shown in Figure 51.8.
You assign a name to your host configuration in the SNA Server Configuration Wizard.
The SNA Server Configuration Wizard window shown in Figure 51.7 enables you to specify the name of an AS/400 connection. The AS/400 connection name can be any value that you choose. The AS/400 connection name will be the name of the remote LU associated with the AS/400. In Figure 51.8, the AS/400 system has been assigned the name S101AA0A. Clicking the Next button displays the SNA Server AS/400 Connection Wizard dialog box shown in Figure 51.9.
Select the Link Service.
The AS/400 Link Service dialog box enables you to select the link service that this SNA Server configuration will use to connect to the IBM host. The Link Service represents the physical connection to the host (802.2 LAN, SDLC coaxial, Channel, and so on). To appear in the Select Link Service drop-down box, the Link Service must have been configured before running the Configuration Wizard. Because SNA Server can support multiple Link Services, the Select Link Service drop-down box in this dialog box enables you to pick the Link Service that you want to use to connect SNA Server and the AS/400. In Figure 51.9, you can see the 802.2 Link Service, SNADLC1, which was created earlier. Clicking the Next (ALT-N) button displays the AS/400 Control Point Wizard dialog box, shown in Figure 51.10.
Enter the AS/400's Control Point Name.
The SNA Server Configuration Wizard window shown in Figure 51.10 enables you to specify the network and control point name of the AS/400 system that you want to connect with SNA Server. The prompt for network name uses the AS/400 default value of APPN. The value entered into the Network Name prompt must match the AS/400's network name. Likewise, the value entered in the prompt for Control Point Name must match the AS/400's local control point name. In most cases, this will be the same as the AS/400's system name. You can find the AS/400's network name and the AS/400 system name by running the DSPNETA command on the AS/400. In Figure 51.10, you can see that this example configuration uses a network name of APPN and a control point name of S101AA0A. Clicking the Next button displays the AS/400 Configuration Wizard dialog box shown in Figure 51.11.
Enter the AS/400's 802.2 adapter address.
The SNA Server Configuration Wizard dialog box shown in Figure 51.11 enables you to enter the AS/400's adapter address and the SAP to be used. The AS/400 adapter address is a 12-digit number that was either burnt into the adapter or overridden when configuring the AS/400's line description. You can find the AS/400's adapter address by running the WRKCFGFSTS *LIN or WRKLIND command on the AS/400 host.
NOTE: As a general rule, you should always override the AS/400 adapter address. If you do not and the AS/400's network adapter fails, then all of the networked systems that are connected to the AS/400 (such as SNA Server and other 802.2 connections) must be reconfigured to use the new AS/400 adapter address before it can reconnect to the AS/400. Overriding the AS/400's adapter address enables you to avoid the extensive network reconfiguration that would be necessary in the event of an AS/400 adapter failure. If you use an overridden AS/400 adapter address, then when the AS/400's adapter is replaced, you can simply reapply the override to the new AS/400 adapter. For Ethernet 802.2 connections, the overridden address must fall within the range of 020000000000-7EFFFFFFFFFF. For Token-Ring 802.2 connections, the overridden address must fall within the range of 4000000001-40007FFFFFFF.
For most installations, the SAP can remain at the default value of 04. Again, like the SAP that was used in the SNA Server Link service configuration, alternate host SAP values are generally used when the host is using multiple network adapters. You can find the AS/400 SAP value by running the WRKCFGFSTS *LIN or WRKLIND command on the AS/400. For example, if the AS/400 is using a line description named ETHLIN1, then you would enter the following command to discover the adapter address and/or SAP value:
WRKLIND ETHLIN1
After configuring the adapter address and SAP value, clicking the Next button displays the final AS/400 Configuration Wizard dialog box (see Figure 51.12).
The final AS/400 Wizard dialog box is a confirmation screen.
This confirmation screen shows the local and remote LU names used in the SNA Server configuration. The Connection name matches the values entered on the third Configuration Wizard dialog box and is the name that the SNA Server Manager will use to represent this configuration. The remote LU name refers to the AS/400 control point name and matches the value that was entered on the fifth AS/400 Configuration Wizard screen. The local LU name refers to the local SNA Server system and is defaulted to the value of Local. If any of these values is incorrect, you can click the Back button to step back through the earlier Configuration Wizard dialog boxes.
Clicking the Finish button generates the SNA Server configuration file that contains all the values specified in the AS/400 Configuration Wizard. After the SNA Server configuration file has been generated, you're prompted to save the new configuration values and restart SNA Server.
After the SNA Server system has restarted, you can start the SNA connection by right-clicking the new S101AA0A connection object that's displayed in the SNA Server Manager. Right-clicking the connection object brings up the SNA Service context menu.
This pop-up menu enables you to start and stop an SNA Server connection. You also can use the Insert option to create a new SNA Server connection object or the Properties option to edit the configuration values of an existing SNA Server connection. Selecting the Start option from the SNA Service context menu starts the SNA Server connection. If all the configuration values are correct, the connection status changes from Inactive to Pending and finally to Active.
The only AS/400 configuration object that must exist in order to connect with SNA Server over an 802.2 connection is the Line Description. In most cases, the AS/400 Line Description already exists. Otherwise, you must create one by using either the CRTLINETH (Ethernet) or the CRTLINTRN (Token-Ring) commands. All of the other AS/400 configuration objects are created automatically when SNA Server first connects to the AS/400.
After SNA Server's connection has been started, you can verify the connection by using the 5250 applet, which applet can be started from SNA Manager's Tools menu. The 5250 applet starts a host 5250 emulation session. Figure 51.13 shows SNA Server's 5250 applet connected to an AS/400.
You use the 5250 applet to verify the connection to the host.
Although the 5250 and the 3270 applets can be run from the SNA Server system itself, they are very simple emulator programs that are not as full-functioned as other IBM and third-party emulation products. The real purpose of the 3270 and 5250 applets is just to verify the connection.
After the SNA Server system has been successfully connected to the IBM host, the client systems can be installed. SNA Server clients are typically installed by using the SNA Server installation CD or by copying the client installation software from the SNA Server installation CD to a shared directory on the Windows NT Server's file system; the clients then run Setup from the shared directory.
If you install the SNA Server client from a network drive, you must first copy the client installation directories from the CD to the target directory. There's a different CD subdirectory for each processor type:
| Client Type | Processor | Installation Directory |
| MS DOS | Intel | \clients\msdos |
| Windows 3.1 | Intel | \clients\win3x |
| OS/2 | Intel | \clients\os2 |
| Windows NT | Intel MIPS DEC Alpha PowerPC |
\clients\winnt\i386 clients\winnt\mips clients\winnt\alpha clients\winnt\ppc |
The minimum system requirement differs for each of the SNA Server clients:
| Client | Protocol | RAM | Hard Disk |
| Windows NT | Named Pipes IPX/SPX TCP/IP Banyan VINES |
14M | 7M |
| Windows 95 | Named Pipes IPX/SPX TCP/IP Banyan VINES |
8M | 6M |
| Windows 3.x | Named Pipes IPX.COM TCP/IP Banyan VINES |
4M | 4M |
| MS DOS | LAN Manager IPX.COM Banyan VINES |
640K | 2.2M |
| OS/2 | Named Pipes | 8M | 1M |
To run Setup from the CD, select the Client Setup option from the CD's Installation menu. When run from the CD, the SNA Server client Setup automatically selects the correct client setup program. When the SNA Server client first begins, it asks the user for his user ID, company name, and destination directory to install the client software. Next, the SNA Server client installation program prompts the user to select the desired client components. The Client Component Select dialog box is shown in Figure 51.14.
Select the SNA Server client components.
The SNA Server 3.0 client includes applets for the SNA Server Manager, 3270 Emulation, 5250 Emulation, Open Database Connectivity (ODBC), and an APPC File Transfer Protocol (AFTP) applet.
NOTE: There are a couple of restrictions about the SNA Server client applets. The SNA Server Manager applet is only available for Windows NT clients, and the AFTP applet is not available for Windows 3.1 clients. In addition, SNA Server's applets are all intended as setup and diagnostic tools--as such, they're licensed for use by only one user at a time.
The next client setup screen enables you to choose the network protocol used to connect to the SNA Server system. Figure 51.15 shows the next client protocol setup window.
Select the protocol for the SNA Server client.
When this configuration dialog box is displayed, options for all of the networking protocols that are installed on the client will be enabled. If a protocol is not installed on the client, the selection is grayed out. After selecting the appropriate protocol, a client installation dialog box prompts the user for the Client Mode. The client defines if it will use a local SNA Server (in the same domain) or a remote SNA Server (in a different domain).
The SNA Server client installation process finishes with a dialog box that prompts the user for the primary and backup SNA Server systems (see Figure 51.16).
Select the primary SNA Server system for the client.
The name of the primary SNA Server must be entered in the Primary prompt. If there is a backup SNA Server, enter its name in the Backup prompt. If there is only one SNA Server on the network, leave the Backup prompt blank.
The SNA Server client setup can also be automated by using an SNASETUP.INI file in conjunction with running the Setup program by using the /q command-line option, as follows:
setup /q
Listing 51.1 shows an example SNASetup section of SNASETUP.INI that performs an automated installation by using the TCP/IP protocol to communicate with a primary SNA Server system named TECA.
[SNASetup] RunInBatchMode=yes LicenseMode=PerServer LicenseUsers=25 InstallTCPIP=yes InstallMicrosoftNetworking=yes InstallNovellNetware=no InstallBanyanVines=yes SNADomainName= LocalDomain=yes RemoteDomain=no PrimaryDomainName=TECA BackupDomainName= YourName=Michael Otey CompanyName=TECA Inc. ProductID= WindowsVersion=WindowsNT351 ServerUserId= ServerPassword= DestinationPath=C:\SNA [ServerOptionalComponents] InstallSNAExplorer=yes InstallODBC=no InstallAFTP=yes Install3270applet=yes Install5250applet=no InstallHostSecurity=no
After the SNA Server client software has been installed, you can use it to connect to the SNA Server system and then the IBM host. To connect the 5250 applet to an IBM AS/400 by using the SNA Server configuration example created earlier and shown in Figures 51.12 through 51.17, you must set the 5250 applet's session properties. The 5250 applet's configuration screen is shown in Figure 51.17.
Configuring the 5250 applet.
On this configuration screen, two drop-down boxes list the local and remote LUs that were created during the SNA Server configuration. The local LU name must match the name of the LU that was assigned to the SNA Server with the Configuration Wizard. If you refer to Figure 51.18, you can see that the SNA Server system used the LU name Local. The remote LU name refers to the LU name of the AS/400. In Figure 51.17, you can see that the AS/400 was assigned the LU name S101AA0A. After you enter the appropriate LU names and restart the 5250 applet, the applet will be able to connect to the AS/400.
Although the real function of SNA Server is behind the scenes, supporting client connections to an IBM host, all of the configuration, administrative, and diagnostic functions can be performed by using the SNA Manager graphical user interface. The SNA Server Manager can manage both the local SNA Server system and multiple remote SNA Server systems.
In the "Setup and Configuration" section, you learned how to use the SNA Server Manager to configure SNA Server and to monitor the status of a connection. The SNA Server Manager is also used to perform the administrative functions for SNA Server. For instance, it's used to perform security functions such as granting user authorities.
Figure 51.18 shows the SNA Server Manager's User and Group Security dialog box.
Add the Everyone User Group in the SNA Server Manager's User and Group Security dialog box
User rights to SNA Server must be granted before client systems can connect to an IBM host by using SNA Server. SNA Server is able to work with security authorization at either the individual user level or at the group level. The simplest security scheme that you can use to connect all of your networked clients to an IBM host is to grant authority to the group Everyone, as shown in Figure 51.18.
After granting authority to the group Everyone, all SNA Server client systems will be able to use SNA Server to connect to the host. Although granting rights to the Everyone group isn't the right answer for most installations, it can be used to quickly connect your client systems. A member of the Administrator group can change the security used by SNA Server later.
Using the group Everyone is a good choice when initially setting up SNA Server because it simplifies the process of connecting the users. Unless you really want to provide all of your network users with host access, however, the group Everyone probably provides more host access than you really want to allow. After you've successfully made several client connections, consider adding to SNA Server's security only the specific users whom you want to access the host or consider creating a new Windows NT user group that combines those users who need host access. Chapter 21,"Administering Users and Groups," provides more information about creating NT users and groups.
Apart from the tools that are found in the SNA Server product, SNA Server is also integrated with the system management tools that are built into Windows NT. The Windows NT Performance Monitor is able to provide statistics about a number of SNA Server communications connections. In addition to the Performance Monitor, SNA Server also logs important events into the Windows NT Application Event Log. Figure 51.19 shows several SNA Server events logged into Windows NT's Application Event Log. Chapter 38, "Monitoring NT Server," contains more information about using NT's Performance Monitor.
The Application Event Log keeps track of important SNA server events.
Windows NT provides three different event logs: the System Log, the Application Log, and the Security Log. SNA Server records its events into the Application Log. The Windows NT Event Log records the event's time, source, and error number. To troubleshoot SNA Server problems or to get more information about the history of an SNA Server connection, you can view the entries in the Application Event Log. Double-clicking any of the SNA Server Event Log entries provides additional information about the nature of the event. You can find more information about the Windows NT Event Log in Chapter 18, "Administering the Server."
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