Interoperability with IBM Host Systems
Interoperability with IBM Host Systems |
|
TN3270 is a type of Telnet service that allows access to mainframe computers over a TCP/IP network. Users can connect to mainframes using a TN3270 client and the TN3270 service provided with SNA Server, as shown in Figure 10.11.
The TN3270 service supports the following protocols:
The TN3270 service uses SNA Server features to provide mainframe access and to address issues such as security and redundancy when the data communications path between the client and server contains one or more unsecured segments.
Figure 10.11 TN3270 Communications Through SNA Server
Because the TN3270 service communicates with SNA Server using the LUA API, LUA-type connections and LUs must be configured on the server. Once configured, LUAs and LU pools can be assigned to the TN3270 service and made available for use by TN3270 clients requesting mainframe access.
As with all TCP/IP services, TN3270 requires a free TCP port in which clients can locate the TN3270 service. The TN3270 service defaults to port 23, the same port as standard Telnet services. Because no two services can share the same TCP port, it is recommended that you change the TN3270 service to use TCP port 24 or some other unused TCP port. When attempting to connect to the TN3270 service from a client application, you must also specify the new TCP port within the application's connection settings.
As described in "SNA Server Integration with Windows 2000–based Networks" earlier in this chapter, a Windows 2000 domain can contain one or more SNA Server subdomains. Like 3270 LUs, LUA LUs from multiple servers in different subdomains can be assigned to the TN3270 service. This allows you to distribute client sessions among the participating servers in the subdomain, thereby balancing the load.
Creating redundant connections to the mainframe and assigning them to a TN3270 service increases service availability. If one server fails, a client can still access LUA LUs on a different server. If no other SNA Server–based computers are used in a particular site, you can increase fault tolerance and available bandwidth by configuring a single server with redundant host links.
Just as you can assign 3270 LUs to a user or workstation, you can restrict access to LUA LUs or pools by specifying an IP address or subnet mask for clients that must access the resource. If a workstation has a name that can be resolved using name resolution services like DHCP, DNS, or WINS, the name can be associated with the resource instead of the individual workstation. For information about TCP/IP addressing and services, see the TCP/IP Core Networking Guide.
Restricting access to clients with specific IP addresses or workstation names increases the security of the LUA resources. For more information about host security issues, see "LAN-to-Host Security" later in this chapter.
