Abracadabra!: Turning an IBM Netfinity Server into a High-Performance Intranet Controller

Today, most mainframe installations are increasingly interested in TCP/IP implementation and connnecting the intranet and Internet to their enterprise systems to access their legacy data and applicatios. This is where the Netfinity ESCON Adapter offers capabilities not found in other channel-attach products, TCP/IP Direct Connect and the Multi-Path Channel (MPC+) drivers.

As part of the Options by IBM product line, the Netfinity ESCON Adapter provides a PCI-to-ESCON connection between your Netfinity server and your IBM or compatible mainframe.

Once connected, there are a number of SNA and TCP/IP connection types supported across this 17 Mbyte/sec link. The Netfinity ESCON adapter ships with a CD-ROM that provides adapter drivers for both Windows NT and NetWare. Data Link drivers are included for the industry’s leading SNA gateways including IBM’s Communications Server for Windows NT, Microsoft’s SNA Server, and Novell’s Netware for SAA.

Today, most mainframe installations are increasingly interested in TCP/IP implementation and connecting the intranet and Internet to their enterprise systems to access their legacy data and applications. This is where the Netfinity ESCON Adapter offers capabilities not found in other channel-attach products, TCP/IP Direct Connect and the Multi-Path Channel (MPC+) drivers. These two extremely valuable Windows NT drivers are a part of the standard offering with each Netfinity ESCON Adapter.

TCP/IP Direct Connect

The TCP/IP Direct Connect establishes a virtual point-to-point connection between the TCP/IP stacks of a Windows NT server and a mainframe. The TCP/IP Direct Connect driver was developed to be Network Driver Interface Specification (NDIS) compliant. As such, the TCP/IP Direct Connect allows the Netfinity ESCON Adapter to appear to Windows NT exactly like any other Network Interface Card (NIC).

Windows NT is capable of performing "static routing" via its IP Forwarding feature. As its name implies, IP Forwarding "routes" IP data between LAN adapters (i.e., Ethernet to token-ring). Since the ESCON adapter with TCP/IP Direct Connect appears as a standard NIC, NT will "route" data from the LAN to the ESCON adapter, and subsequently to the mainframe. The benefit is that any workstation on the network can gain immediate Telnet and FTP access to applications and files on the mainframe.

Figure 1 shows a simple network made up of two sub-networks connected by a router. A single Windows NT server is installed on the token-ring. Windows NT, 95, or 98 is installed in all workstations.

An IP subnet mask of is being used to allow for 4 subnets with IP addresses as follows:

Subnet 0 -

Subnet 1 -

Subnet 2 -

3 -

As shown, the Ethernet segment makes up Subnet 0 and the token-ring makes up Subnet 1. Subnets 2 and 3 are currently not used. The router’s Ethernet port is assigned an IP address in Subnet 0 and the token-ring port is assigned an address in Subnet 1.

Workstations on the Rthernet LAN are configured with their Default Gateway set to Workstations and the server on the token-ring have their Default Gateway set to

Adding a TCP/IP link to a mainframe from the server in this environment is easy and straightforward. Figure 2 shows how the network might look after an ESCON adapter with TCP/IP Direct Connect has been installed.

Notice that a new IP address has been assigned to the TCP/IP Direct Connect ( and to the Mainframe ( The TCP/IP Direct Connect address and the Mainframe address must both be in the same subnet in order for Windows NT TCP/IP to establish static routing with the mainframe and be able to send TCP/IP traffic across the link. If the mainframe were in a different subnet than the TCP/IP Direct Connect, TCP/IP would incorrectly attempt to identify an IP address for a gateway, in order to get to the mainframe.

Notice also that these two addresses are in their own subnet, Subnet 2, which was unused before the ESCON adapter was installed. This is an important point: As long as the server’s LAN adapter ( is in a separate subnet from the TCP/IP Direct Connect, Windows NT will automatically build a static route to move IP traffic between adapters when Enable IP forwarding is turned on (in TCP/IP Properties). However, if the TCP/IP Direct Connect and LAN adapter are in the same subnet, moving packets between the two would require a bridging function, which Windows NT Server does not perform.

To complete the network configuration, a static route would be added to the router between the Ethernet and token-ring LANs that redirects all traffic destined for (the mainframe) to (the server).

Since all workstations on both LANs define the router as their default gateway, they will go to the router when they want to attach to the mainframe (because the mainframe and workstations are in different subnets). Workstations on the Ethernet LAN will automatically be forwarded to the server by the static route information in the router tables.

For workstations on the token-ring, the router will see that the server and workstation are in the same subnet and send an Internet Control Message Protocol (ICMP) Route message to the workstation to update its route information. Future packets destined for the mainframe will be sent directly from the workstation to the server (

In most existing networks today, it will not be necessary to update the TCP/IP configuration on the workstations in order to allow them to connect to the mainframe using an ESCON adapter with TCP/IP Direct Connect. Most workstations already point to an existing router and/or server as a default gateway, and that will be all that is needed.

The one notable exception to that rule is a single-segment LAN with no gateways. In that unlikely situation, it may be necessary to modify the TCP/IP properties for all workstations requiring access to the mainframe through the TCP/IP Direct Connect gateway.

Once TCP/IP Direct Connect is installed and configured, all clients and servers have TCP/IP access to the mainframe. TN3270 and FTP applications running on the client gain immediate access to applications and files on the S/390.

Additionally, TCP/IP applications, such as IBM’s DB/2 Enterprise Connect, can be distributed to any server and client in the network. Enterprise resource planning (such as SAP, PeopleSoft) and business intelligence (e.g., data warehousing, data marts) applications, which rely on DB/2 Connect to retrieve data from the mainframe’s DB/2 database, will gain improved performance through the ESCON channel.

Multi-Path Channel (MPC+)

If TCP/IP Direct Connect is not enough to convince you that this is the way to connect your network to the mainframe, then perhaps MPC+ will help win you over.

MPC+ is an IBM strategic technology, which offers a reliable, high-performance channel protocol that significantly reduces mainframe CPU cycles consumed while performing channel operations. MPC+ in OS/390 offers support for both TCP/IP and SNA communications.

The MPC+ driver is included with the Netfinity ESCON Adapter and works with OS/390 Version 2 Release 4 and above. It provides support for TCP/IP User Defined Protocol (UDP) applications and has been certified with SAP’s R/3 solution for the S/390.

SAP R/3 for the S/390 is a three-tiered business applications solution where the S/390 is the database server, a Windows NT Server runs the SAP R/3 applications and the network attached client runs presentation services (see Figure 3). The Netfinity ESCON Adapter with MPC+ allows specialized database access routines provided as part of the SAP R/3 for S/390 solution to access DB/2 across the ESCON channel using UDP protocols.

To support SAP R/3 in this fashion MPC+ is used as a data link for TCP/IP Direct Connect. Together they provide High-Speed Access Services (HSAS) (formerly referred to as High-Performance Data Transport, or HPDT, for UDP) across the channel.

Finally, by combining these features with the IP forwarding capability of the Windows NT Server, it becomes possible to distribute the SAP R/3 applications themselves to any NT Server in the network. The data requests are then routed back to the ESCON-attached server for resolution (see Figure 4 ).


At first glance, the IBM Netfinity ESCON Adapter includes support for market-leading SNA gateway products like Communications Server for Windows NT, SNA Server, and NetWare for SAA. However, the Netfinity ESCON Adapter does not stop there.

Included with every Netfinity ESCON Adapter are the TCP/IP Direct Connect and MPC+ drivers, which allow the mainframe to communicate with Windows NT in point-to-point fashion using TCP/IP.

The key to the TCP/IP Direct Connect driver is that it was designed to be NDIS-compliant. This presents the ESCON adapter as a standard NIC to Windows NT. The net result is that any application that is running on a Windows NT Server and uses TCP/IP as its protocol can gain access to mainframe resident data.

MPC+ permits you to combine the bandwidth of two or more separate ESCON channel connections into a single transmission group. This feature not only provides high-performance throughput and error-free transmissions, but also provides automatic failover in case one of the ESCON connections are lost.

So, if you have a S/390 class mainframe and are building corporate intranets, you really cannot afford to ignore this emerging technology.

About the Author: Ralph Armstrong is Vice President of Product Management for Bus-Tech Inc. in Burlington, Mass.